sat virtual reality iii explanations phần 4 pps

Passage 1 talks about the difficulty of reconstructing or replacing certain bones in humans.. The author is not objective and impartial; he’s taking a stand on an issue: he argues that t

Now look at the answer choices The only one that is true is (E), which states that the median of the scores is equal to the mean

11 C Check the statements one at a time Start with Statement I The sum of the

measures of the angles of a triangle is 180 degrees, and the small triangle has angles

measuring a, b, and 90 degrees Therefore, a + b + 90 = 180 Subtracting 90 from both sides leaves you with a + b = 90, so I is true Move on to Statement II Because lines 3 and 4 are parallel and d and a are corresponding angles, you know that d = a Now you need to decide whether the sum of the measures of d and c equals 90 degrees Notice that d and c are part of a large right triangle Therefore, as with Statement I, d + c + 90 = 180, so d + c = 90 Since a = d, you know that a + c = 90

and that Statement II is also true Now try Statement III There is no information that

tells you that b is equal to either a or d, or that any of the line segments are of equal length Therefore, there is no way of knowing whether b and d are equal They may

be, but it is also possible that they are not Therefore, only I and II must be true and the answer is (C)

12 C If there are 200 mattresses in the store, you can subtract the sum of the twin-, full-,

and king-sized mattresses from 200 to find the number of queen-sized mattresses currently in stock:

There are 70 queen-sized mattresses When there are 70 mattresses of each size, there will be 70 × 4 = 280 mattresses total There are currently 200 in stock, so you need 80 more

13 D The best way to do this problem is to use common sense If there were 4 chairs at all

25 tables, there would be 100 total seats If there were 1 table with 2 chairs and 24 with 4 chairs, there would be (24 × 4) + 2 = 96 + 2 = 98 chairs Therefore, for every

1 table with 2 chairs, you lose 2 chairs from the sum The total of 86 chairs in the restaurant is 14 less than the 100-chair maximum 14 ÷ 2 = 7, so there are 7 tables with 2 chairs and 18 tables with 4 Double-check this by computing (18 × 4) + (7 × 2)

= 72 + 14 = 86

Another way to do this problem is by backsolving Plug the answer choices into the following equation:

4t + 2(25 – t) = 86

Start with choice (C) since it’s in the middle:

4(15) + 2(25 – 15) = 60 + 20 = 80 That’s too few chairs You have to try a bigger choice Try (D):

= 200 − 130 = 70

SAT

Virtual Reality III

34

4(18) + 2(25 – 18) = 72 + 14 = 86

It works! Either way you approach this problem, the answer is (D)

14 D The most important part of this question is knowing which of the coordinates are

positive and which are negative Look at the diagram again:

Remember that the x values are the first coordinates in a pair and the y values are the

second coordinates Values for x are positive if they are to the right of the y-axis and

are negative if they are to the left Values for y are positive if they are above the

x-axis and are negative if they are below it Following these rules, the positive values

must be d, b, and a The negative values must be c, e, and f Now all you have to do

is go through the answer choices and find two variables with the same sign that are

multiplied together The only such choice is ef, choice (D).

15 C First figure out how many miles will be traveled at each price There are 100 miles

total, and the first 10 cost a flat rate of $5.00 That leaves 90 miles, 40 of which cost

$0.25 per mile The last 50 miles cost $0.10 per mile Now find out how much each

segment costs and add them together:

16 C The formula for the area of a triangle is the following:

Area = Base × Height

In this problem, you are told that the area of the triangle is 24 and that the height is 6

You can also tell from the diagram that the base is equal to x + (x + 2) Now

substitute these values into the area formula:

x = 3

1 2

SAT

Virtual Reality III

35

(c, d ) (a, b)

(e, f )

x y

17 A Begin with Statement I Look at the inequality that states x – y > 0 Adding y to both

sides gives you x > y, so Statement I must be true Move on to Statement II, which states that x and y are both positive Now look at the first inequality, x + y < 0 If the sum of x and y is less than 0, it is impossible for both numbers to be greater than 0 Therefore, Statement II cannot be true Now try Statement III This says that x must

be positive and y must be negative The best way to test this statement is to pick numbers If x = 2 and y = –3, x + y = –1, which is less than 0, and x – y = 5, which is greater than 0 In this case, Statement III is true But what if x and y are both

negative? What if x = –2 and y = –4 ? Using these values, x + y = –6, which is less than 0, and x – y = 2, which is greater than 0 Since x can be either positive or

negative, Statement III is not necessarily true and the answer is (A)

18 B All you need to do in this problem is plug a = 6 and b = 4 into the expression and

evaluate it:

19 E This problem is a bit more involved than the last one using the same operation, but

still uses the same concepts Instead of simply substituting one set of values into the expression and computing, you must substitute 2 sets of values into the expression,

set them equal to each other, and solve for a Substituting the given values into the

expression and setting them equal to each other gives you:

20 B The first step to solving this problem is getting both ratios into a form that has the

same value for a If a : b = 4 : 5 and a : c = 2 : 7, you can make both values of a 4 by multiplying the entire a : c ratio by 2 The new form of the ratio becomes 4 : 14 Now you can compare b and c Be careful, however, because the question asks for c : b,

not the other way around Therefore, the ratio is 14 : 5 or , choice (B)

21 A The easiest way to do this problem is to try some values for x and see which is the

greatest power of 4 that is less than 250 Since you have to calculate 43to raise 4 to higher powers, you should start there 4× 4 × 4 = 64, which is less than 250 Multiply this number by 4 to find 44 64 × 4 = 256, which is greater than 250 The greatest power of 4 which yields a number less than 250 is 3, choice (A)

14 5

a2 − a

2

a(a− 1)

2

a− 1= 98

2

a = 50

a2 − b

SAT

Virtual Reality III

36

22 D To figure out how many tiles are needed, you must break up the L-shaped floor into

sections This will allow you to work with rectangular areas instead of an odd shape

Break the room up like this:

Now you must find how many tiles are needed to cover each rectangle Since you

have the dimensions of each tile in terms of x and y, you can figure out how many

tiles are needed by picking numbers for x and y To make life easier, use x = 25 and y

= 20 Now calculate the dimensions of a tile and of the room and relabel the diagram:

Now the tile is 1 by 1 and the room’s two areas are 5 by 25 and 15 by 5 Find the

areas of the 2 sections of the floor, add them together to get the total area of the

bathroom floor, and, since the area of a tile is 1, you have your answer:

You would normally divide this number by the area of one tile, but since the area of a

tile is 1, 200 ÷ 1 = 200 and the answer is (D)

23 D The first thing you need to do is find what the tens’ digit can be You are given that

the sum of the other two digits must equal the square of the tens’ digit and that the

hundreds’ digit must be 3, 2, or 1 Therefore, the greatest possible sum of the

hundreds’ and tens’ digits is 3 + 9, or 12 The square of the tens’ digit must be 12 or

less, and the only perfect squares less than 12 are 0, 1, 4, and 9 Since there is no

way the hundreds’ digit can equal 0, you can eliminate 0 as an option The tens’ digit

can either be 1 = 1, 4 = 2, or 9 = 3 Now count the combinations of numbers

= 125 + 75

= 200

5

5

25

15

SAT

Virtual Reality III

37

x

y 4

x 5

3 4

between 100 and 400 in which the sum of the hundreds’ digit and the units’ digit equals 1, 4, or 9 The easiest way to do this is to list the possibilities:

There are 7 possibilities, choice (D)

24 B Use algebra to find the solution to this problem First, find the numerical values for b

and c Since 2b = 7, divide both sides of the equation by 2 and you get b = Do

the same thing with 3c = 7, giving you c = Now plug these values into the first equation:

Now solve for :

25 D This one is hard to draw Think logically and try to visualize the orange The first cut

breaks the orange into 2 pieces If you cut the orange so that you cut the 2 halves into equal pieces, you have 4 equal quarters Your next cut can cut the quarters into 8 equal pieces Therefore, 3 cuts can yield a maximum of 8 pieces, choice (D)

3





6



21

x y

x = 1 6

y x

3



7 3

7 2

SAT

Virtual Reality III

38

Section 6 (Verbal)

Medical Pair

Although these two passages discuss issues in medical research, don’t be

intimidated by the subject matter Read through the passages once to get a

general feel for them The question stems will direct you back to the specific

sentences you’ll need to understand to get the answers Also, it’s a good idea to

read through Passage 1 and do the questions that refer to it, and then read

through Passage 2 and do the rest of the questions

Passage 1 talks about the difficulty of reconstructing or replacing certain bones in

humans A recent advance has been the creation of bone substitutes from muscle

using the protein osteogenin While osteogenin can’t be used directly on a defect,

it can be used to prefabricate bones in molds implanted in an animal’s abdomen

The process hasn’t been tried in humans, though, because osteogenin is scarce,

and because it has to be tested on larger animals first

Passage 2 has a distinctly different tone The author is not objective and impartial;

he’s taking a stand on an issue: he argues that testing on humans is necessary in

order to make improvements in artificial organs Using animals, he says, isn’t good

enough: there are no good animal models for human bones and joints Moreover,

testing on humans gives doctors crucial experience The author concludes that

there’s no point in developing new designs for artificial organs until present ones

have been evaluated on people

1 D Remember to read the sentences before and after the line reference At the end of

paragraph 1, the author talks about the difficulty of reconstructing and replacing

bones This is the “challenge” that’s further explained in paragraph 2—(D) is the

answer The author doesn’t mention tissue development in the human embryo

until paragraph 3 (A) (B) contradicts the passage: the author states that it ’s

impossible to reconfigure bones It’s currently possible to replace joints with plastic

or metal substitutes, but the author never says anything about designing better

types of them (C) She never identifies “the causes of diseases that lead to bone

losses” (E) either

2 E The stem contains no line reference, but the only place the author talks about

future experiments in making bone from muscle is the last paragraph She says

there that surgeons “have not yet tried the process in humans” and that it “must

first be tested on larger animals.” The author expects, therefore, that future

experiments will “involve larger animals and perhaps humans” (E) There’s no

evidence that future experiments will “encounter no serious problems” (A), that

they will be hindered by surgeons (C), or that they “face enormous technical

obstacles” (D) And despite the fact that all experiments have so far been limited

to smaller animals (B), it’s clear that this isn’t what the author expects in the

future

3 C An example of the all/EXCEPT question type Information about osteogenin is

spread over the last three paragraphs, so scan through the choices to see if one

jumps out before you start digging through the passage (C), “its application can

SAT

Virtual Reality III

39

be easily controlled,” should strike you as false because the author says in paragraph 4 that osteogenin is hard to control—it might turn an entire area to bone

if sprinkled on a defect If you didn’t spot (C), you had to confirm the other choices

“Current supplies [of osteogenin] are limited” (A) is indicated in paragraph 6 This

is also where the author says that “tests of its effectiveness have been limited” (B)

to small animals, and that osteogenin’s “safety for human use is undetermined” (D) The fact that “some surgeons hesitate to use it” (E) because it’s hard to control is stated in paragraph 4

4 A You’ve already had to go back and read through the last paragraph a couple of

times by now, so glance through the choices “A review of current knowledge” (A) looks good right away, because the author points out in the last paragraph how far surgeons have gone in experimenting with and learning about the new process There’s no “qualification of an earlier remark” (B) (C) is out because the author never mentions, no less challenges, a contradictory view The final paragraph presents new facts and ideas rather than a “summary of previous ideas” (D) As for (E), the author’s call for testing on larger animals is a demand not “for an

alternative approach” but for a guarantee of safety and effectiveness before the process is tried on people

5 D The phrase “to die young at a ripe age” doesn’t make much sense until you

understand its context The author’s discussing the eventual benefits of artificial organs: ordinary people can live longer or, even better, they can die young at a ripe age “Dying young at a ripe age” does not mean “living longer” (E) Nor does it mean “dying prematurely” (A), “dying young of an illness” (B), or “extending one’s life despite being ill” (C)—none of these is a positive thing—the author’s talking about the benefits of artificial organs “Dying young at a ripe age” means dying at

a normal old age after having enjoyed a relatively young body during your life; in other words, it means “maintaining a healthier body into old age” (D)

6 C In paragraph 2 of Passage 2, the author accuses medical ethicists of hampering

the activities of human volunteers He declares that the ethicists are “well-intentioned” but “their standards are inappropriate.” Clearly, the author is

“disapproving” (C) of them None of the other words comes close to describing the author’s attitude

7 E Looking down through the choices, you can see that the only one that can be

eliminated right away is “slogans” (A), which is not a synonym for standards To pick the right one, go back and locate "standards" in its context The author says that the “standards,” or “principles” (E), of the medical ethicists are inappropriate

“Measurements” (B), “examples” (C), and “banners” (D) don’t make sense in the context of the sentence

8 A Another vocabulary-in-context question Checking the sentence, “critical” is used to

mean “decisive“ (A): the author’s stating that the need to use humans leads to a decisive or very significant “bottleneck in the experimental process.” Critical isn’t used to mean “aggressive” (B), “skeptical” (C), “perceptive” (D), or “fault-finding” (E)

9 A The author discusses the use of artificial heart devices in paragraph 4 The design

of the devices is not a problem, he says; rather, it’s the lack of experience

SAT

Virtual Reality III

40

section six

SAT

Virtual Reality III

41

researchers have had using them with human subjects He points out that heart

devices may work in one patient and not in another, depending on age, health and

the quality of postoperative care He repeats his point at the beginning of the next

paragraph: what’s lacking in coronary care is simply more experience (A) The

author isn’t “praising scientists’ ability to fight coronary disease” (B); he’s saying it

could be much better if human testing were done The author never mentions any

“lingering doubts” about artificial heart implants (C) (D) contradicts the passage

directly: the author says that “engineering design is not currently the main

obstacle.” Finally, (E) is wrong because the author never discusses “several new

treatments now available to heart patients.”

10 C The author poses the questions in the last paragraph in order to identify

information that scientists still lack He’s showing that their knowledge of coronary

disease is incomplete (C)—that’s why human testing is so essential He’s not

illustrating the value of any new devices (A)—he’s opposed at present to new

devices Nobody else’s arguments are being refuted here (B) (D) turns the

author’s ideas around: he supports human testing As for (E), “widely publicized

areas of research” misses the point The point is simple: these are questions that

need to be answered

11 B The answer here has to be fairly general, because the connection between the two

passages is indirect Take the answer choices one by one and evaluate each one

using evidence from the passages For example, (A) is wrong because the author

of Passage 1 doesn’t disagree with anyone or cite any views different from hers

(B), though, is accurate: the author of Passage 1 talks about the difficulty surgeons

have in reconstructing and replacing bones, and the author of Passage 2 laments

surgeons’ lack of experience in using artificial organs (C) and (D) are wrong

because only the author of Passage 2 demands mentions cultural values as a

barrier to research As for (E), neither author advocates a more rapid development

of new implant procedures

12 B Passage 2 is devoted to arguing for the testing of artificial organs on humans,

because restrictions on human testing are a major obstacle to improved devices

Before checking the choices, predict what the author of Passage 2 might say about

the wider use of osteogenin No doubt he’d say that gaining experience with the

use of osteogenin on humans would be difficult—exactly what (B) says (A) and

(D) cite valid obstacles to the wider use of osteogenin, but they’re wrong because

there’s no reason to think that the author of Passage 2 would stress them (C) and

(E) are out because they aren’t obstacles to the use of osteogenin at all

13 D The last paragraph of Passage 1 states that the process of bone prefabrication

has not yet been tried on humans—that it needs to be tested on large animals

first The last paragraph of Passage 2 features questions about coronary care that

can only be answered through human testing In other words, both authors are

stressing the need to “gather information that’s relevant to the treatment of human

patients” (D) (A) is out because neither author sees the need to “develop new and

improved devices for human implantation.” The author of Passage 1 suggests that

experiments should next be carried out on larger animals, which rules out (C),

while the author of Passage 2 wants testing on humans, which eliminates (B) As

for (E), neither author advocates “curbing the growing use of animals in testing.”

section se

SAT

Virtual Reality III

42

Section 7 (Math)

1 D If Thomas wound up in debt, it means that he spent more money than he actually

had — a situation that we’re all familiar with So, the correct answer must be greater than the amount of money he had, which was $15, so eliminate choices (A), (B), and (C) If he has a debt of $5, then he must have spent all the money he had, or

$15, and then borrowed another $5 and spent that also So he spent a total of $15 + $5, or $20, choice (D)

2 D Here, the angle marked x° is in a triangle with 2 other unknown angles However,

one of those unknown angles of the triangle, the one just above the x° angle, lies on

a straight line with an angle measuring 98° Therefore that angle must measure

180° – 98° = 82° The third angle in the triangle is opposite a 54° angle that is formed by the intersection of 2 straight lines So the third angle of the triangle must also measure 54° The 3 angles of a triangle add up to 180°, so 54° + 82° +

x ° = 180°, and x = 44, choice (D).

3 E Since something happens every 5 minutes at this party, let’s look at each five-minute

interval At first there are 256 people After 5 minutes half of them leave That means that 128 people leave and 128 people are left after 5 minutes 5 minutes after that, or 10 minutes after we started, half the remaining people leave That means that half of 128, or 64, people leave and 64 are left after 10 minutes At 15 minutes after the start, half the remaining 64, or 32, people leave and 32 people are left At 20 minutes after the start, half of 32, or 16, people leave and so finally only

16 people are left to eat all those ham and cheese sandwiches from section 2 Answer choice (E) is correct

4 A Remember, in a symbolism problem you shouldn’t worry that there’s a strange

symbol you’ve never seen before It’s just a made-up symbol that is always defined

by mathematical concepts that you’ve seen before Here, an x with a circle around it just means to plug x into an equation If x = 5x – , then 8 = 5(8) – , or

40 – 4, which is 36, answer choice (A)

5 C You have 6 chairs and 4 people Go through your rules one at a time and make

deductions accordingly You'll want to start with the following sketch:

1

2

3 4

5 6

8

 2

x

 2

Rule 1 - Ruth occupies Chair 2

Rule 2 - No one sits next to Quincy

Deduction - Quincy does not sit in chair 1 or 3

Rule 3 - Peter sits between Ruth and Sarah

6 B If a rectangle has a perimeter of 12 then 2(W + L) = 12, where W is the width of the

rectangle and L is its length If 2(W + L) = 12, then W + L = 6 If the width is 2 less

than the length, then W = L – 2 You can plug L – 2 for W into the equation W + L =

6, so W + L = 6 becomes (L – 2) + L = 6, and so 2L – 2 = 6, 2L = 8, and L = 4 If

the length is 4, then the width, which is 2 less, must be 2 The area of a rectangle

with length 4 and width 2 is 4 × 2 = 8, answer choice (B)

7 C The easiest way to do this one is to just draw lines from each point and then add up

the number of line segments drawn From point A, draw one line to each of points

B, C, D, and E From point B, you already have a line to point A, so just draw a line

to each of points C, D, and E From point C you have already drawn lines to A and

B, so draw in a line to point D and one to point E, and finally draw a line from point

D to point E (You’ve drawn a star inside a pentagon - very artistic!) Can you see

any point that is unconnected to any other point? No, so just add up the number of

lines you’ve already drawn — there are 4 + 3 + 2 + 1 or 10 of them, answer choice

(C)

8 B Whenever you have a word problem that doesn’t give you a definite amount and

asks you a question like “What fraction of the total ?”, you should pick a number

for the total Since you’re dealing with percents here, a good number for the total is

100 So let’s say that 100 people were polled 80% of the 100 people were

registered voters, so 80 people were registered voters 75% of the registered voters

voted in the last election, so 75% × 80, or 60 people voted in the last election If 60

of the 80 registered voters actually voted in the last election then 80 – 60 = 20 of the

registered voters didn’t vote in the last election The fraction of the people surveyed

who were registered but didn’t vote is , or 1, answer choice (B)

5

20

 100

1 P

2 R

3 4

5

S 6

1

2 R

3 P

4 S 5

6

1

2 R

3 4

5 6

SAT

Virtual Reality III

43