SAT Math : Evaluating Expressions

Study concepts, example questions & explanations for SAT Math

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Example Questions

Example Question #1061 : Psat Mathematics

The projected sales of a movie are given by the function s(p) = 3000/(2a) where s is the number of movies sold, in thousands; p is the price per movie, in dollars; and a is a constant. If according to projections, 75,000 cartidges will be sold at $15 each, how many movies are sold at $20 each?

Possible Answers:

20,000

50,000

150,000

200,000

60,000

Correct answer:

60,000

Explanation:

You set up the equation to solve for a.

75 = 3000/(2(15) + a)

= 10

You then set up the formula again for each movie costing $20, s(20) = 3000/(2(20) + 10), and solve for x, the number sold, giving you 60.

Example Question #23 : Expressions

Half of one hundred divided by five and multiplied by one-tenth is __________.

Possible Answers:

2

10

5

1/2

1

Correct answer:

1

Explanation:

Let's take this step by step. "Half of one hundred" is 100/2 = 50. Then "half of one hundred divided by five" is 50/5 = 10. "Multiplied by one-tenth" really is the same as dividing by ten, so the last step gives us 10/10 = 1.

Example Question #21 : Evaluating Expressions

Let x&y be defined as (x – y)xy . What is the value of –1&2?

Possible Answers:

–1/9

3

1/9

–3

–1/3

Correct answer:

1/9

Explanation:

We are told that x&y = (x – y)xy 

–1&2 = (–1 – 2)(–1)(2) = (–3)–2 

To simplify this, we can make use of the property of exponents which states that ab = 1/(ab ).

(–3)–2 = 1/(–3)2 = 1/9

The answer is 1/9.

Example Question #22 : Evaluating And Simplifying Expressions

If 18 – w is 8 less than 32, what is the value of \dpi{100} \small -\frac{1}{3}w ?

Possible Answers:

–6

2

–2

3

–3

Correct answer:

2

Explanation:

We need to rewrite this problem in mathematic terms.

8 less than 32 can be written as 32 – 8

so we will get the equation

18 – w = 32 – 8.

Now, we need to solve for w. 

w = 32 – 8 – 18

w = 6

w = –6

Find the value of the given expression, \dpi{100} \small -\frac{1}{3}w, by plugging in –6 for w.

\dpi{100} \small -\left (\frac{1}{3} \right )\left ( -6 \right )=2

 

Example Question #31 : Expressions

If x and y are integers such that x > y > 0 and x+ y= 100

Which of the following can be the value of x + y?

I. 10

II. 12

III. 14

IV. 16

V. 18

Possible Answers:

16

12

18

14

10

Correct answer:

14

Explanation:

Note that x must be greater than y and that y must be greater than 0. This means that x and y are different, positive integers. In addition, the sum, x+ y2 must equal to 100. If we list squares beginning from the square of the first integer greater than 0 (12) up to the square of the greatest integer less than 100 (92) we will get:

1, 4, 9, 16, 25, 36, 49, 64, 81

We must observe that the only two numbers that will add up to 100 are 36 and 64.

Remember that x > y > 0 and that x+ y=100.

This means that x must be \dpi{100} \small \sqrt{64} and y must be \dpi{100} \small \sqrt{36}

When we solve for x and y we get:

x = 8

and y = 6.

Therefore, x + y can only be 14.

Example Question #21 : How To Evaluate Algebraic Expressions

If m > n, which of the following has to be true?

Possible Answers:

m^{2} > n^{2}

mn > -mn

\left | m \right | > \left | n \right |

\frac{m}{2} > \frac{n}{2}

mn > 0

Correct answer:

\frac{m}{2} > \frac{n}{2}

Explanation:

Plug in numbers for each alternative. If both sides of the inequality \frac{m}{2} > \frac{n}{2} are multiplied by 2, the result is the original inequality, m > n. The other options fail (if confused, try plugging in m as a positive, n as a negative).

Example Question #1061 : Psat Mathematics

Billy began lifting weights in February. After 6 months, he can lift 312 lbs, a 20% increase in the amount he could lift in February. How much weight could Billy lift in February?

Possible Answers:

250\ lbs.

290\ lbs.

270\ lbs.

280\ lbs.

260\ lbs.

Correct answer:

260\ lbs.

Explanation:

1.2w = 312

w = 260 lbs

Example Question #29 : Expressions

A metal rod is 36 inches long and divided into 3 sections. The middle section is twice as long as the first section.  The third section is 4 inches shorter than the first section.  How long are the sections?

Possible Answers:

None of the above answers

The first piece is 15 inches, the second piece is 15 inches and the third piece is 6 inches

The first piece is 6 inches, the second piece is 10 inches and the third piece is 20 inches

First piece is 20 inches, the second piece is 10 inches and the third piece is 6 inches

First piece is 10 inches, the middle piece is 20 inches, and third piece is 6 inches long.

Correct answer:

First piece is 10 inches, the middle piece is 20 inches, and third piece is 6 inches long.

Explanation:

Assume the first section equals x inches, then the second(or the middle section) must be equal to 2x and the third piece must be equal to x-4.

x+2x+(x-4)=36 and now you solve for x which equals 10.  Hence the middle piece must be equal to 20 inches and the third piece is only 6 inches long.

Example Question #30 : Expressions

A               B

1               2

2               4

3               10

5               34 

Using the table above, please select the answer below that expresses the relationship between A and B.

Possible Answers:

B=A^3-2A^2+2A+1

B=2A

B=2A^2-4A+4

B=8A-6

B=A^2+A-2

Correct answer:

B=2A^2-4A+4

Explanation:

By testing the answers, it can be seen that the only equation to satisfy all cases in the table above is

B=2A^2-4A+4

Example Question #33 : New Sat Math Calculator

Fred has $100 in quarters and nickels.  He initially has 260 quarters.  He then exchanges some of his nickels for the dimes of a friend.  He is left with a total of 650 coins (consisting of quarters, dimes and nickels) still worth $100.  How many nickels does Fred have now?

Possible Answers:

Correct answer:

Explanation:

Fred has $100 in quarters and nickels initially.  We are also told that he has 260 quarters.  This is worth $65.  Thus Fred initially has $35 in nickels or 700 nickels.

Fred now exchanges some of his nickels for the dimes of a friend.  He ends up with 650 coins.  We know that Fred started with 960 coins (700 nickels + 260 quarters).  He ends up with 650 coins.  The number of quarters remains unchanged, meaning he now has 390 nickels and dimes.  These must have the same value as the initial 700 nickels, though, since he didn't lose any money.

Now we can finally set up our solution:

Thus Fred has 80 nickels and 310 dimes.

An alternative solution step is to notice that turning nickels into dimes always occurs in exactly one way: 2 nickels to 1 dime.  Every time you do this conversion, you will lose exactly one coin.  We then notice that the number of coins drops from 960 to 650, or drops by 310 coins.  We thus need to get rid of 310 coins.  Since we're only allowed to change nickels into dimes (and lose 1 coin each time), we simply do this 310 times to reach the requisite number of coin losses.  We are left with the proper number of coins with the proper value immediately.  Since every replacement replaced 2 nickels, we also lost  nickels.  Our final number of nickels is thus  nickels.

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