PSAT Math : Arithmetic

Study concepts, example questions & explanations for PSAT Math

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Example Questions

Example Question #241 : Arithmetic

Find the product.

Possible Answers:

Correct answer:

Explanation:

Since we have one positive and one negative multiple, the resulting product must be negative. 

Example Question #1 : How To Subtract Negative Numbers

If x is a negative integer, what else must be a negative integer?

 

Possible Answers:

x – (–x)

x² – x

x – x

Correct answer:

x – (–x)

Explanation:

By choosing a random negative number, for example: –4, we can input the number into each choice and see if we come out with another negative number.  When we put –4 in for x, we would have –4 – (–(–4)) or –4 – 4, which is –8.  Plugging in the other options gives a positive answer.  You can try other negative numbers, if needed, to confirm this still works. 

 

 

Example Question #2 : Negative Numbers

–7 – 7= x

–7 – (–7) = y

what are x and y, respectively

Possible Answers:

y = 0, x = 14

x = –14, y = 0

x = 0, y = 0

x = 14, y = –14

x = –14, y = 14

Correct answer:

x = –14, y = 0

Explanation:

x: –7 – 7= –7 + –7 = –14

y: –7 – (–7) = –7 + 7 = 0

when subtracting a negative number, turn it into an addition problem

Example Question #31 : Integers

Possible Answers:

13

15

16

5

2

Correct answer:

16

Explanation:

Subtracting a negative number is just like adding its absolute value.

Example Question #1 : Even / Odd Numbers

Which of the following could represent the sum of 3 consecutive odd integers, given that d is one of the three?

Possible Answers:

3d – 3

3d + 3

3d + 4

3d – 6

3d – 9

Correct answer:

3d – 6

Explanation:

If the largest of the three consecutive odd integers is d, then the three numbers are (in descending order):

dd – 2, d – 4

This is true because consecutive odd integers always differ by two. Adding the three expressions together, we see that the sum is 3d – 6.

Example Question #1 : How To Add Odd Numbers

\dpi{100} p+r=20, where \dpi{100} p and \dpi{100} r are distinct positive integers.  Which of the following could be values of \dpi{100} p and \dpi{100} r?

Possible Answers:

0 and 20

5 and 15

–10 and 30

10 and 10

4 and 5

Correct answer:

5 and 15

Explanation:

Since \dpi{100} p and \dpi{100} r must be positive, eliminate choices with negative numbers or zero. Since they must be distinct (different), eliminate choices where \dpi{100} p=r.  This leaves 4 and 5 (which is the only choice that does not add to 20), and the correct answer, 5 and 15.

Example Question #1 : Even / Odd Numbers

The sum of three consecutive odd integers is 93. What is the largest of the integers?

Possible Answers:

Correct answer:

Explanation:

Consecutive odd integers differ by 2. If the smallest integer is x, then

x + (x + 2) + (x + 4) = 93

3x + 6 = 93

3x = 87

x = 29

The three numbers are 29, 31, and 33, the largest of which is 33.

Example Question #1 : Even / Odd Numbers

You are given that  are all positive integers. Also, you are given that:

 is an odd number.  can be even or odd. What is known about the odd/even status of the other four numbers?

Possible Answers:

 and  are odd;  is even;  can be either.

None of the other responses are correct.

, and  are odd;  can be either.

 and  are odd;  and  are even.

 ia odd;  and  are even;  can be either.

Correct answer:

 and  are odd;  is even;  can be either.

Explanation:

The odd/even status of  is not known, so no information can be determined about that of .

 is known to be an integer, so  is an even integer. Added to odd number , an odd sum is yielded; this is .

 is known to be odd, so  is also odd. Added to odd number , an even sum is yielded; this is .

 is known to be even, so  is even. Added to odd number ; an odd sum is yielded; this is .

The numbers known to be odd are  and ; the number known to be even is ; nothing is known about .

Example Question #2 : Even / Odd Numbers

You are given that  are all positive integers. Also, you are given that:

 is an odd number.  can be even or odd. What is known about the odd/even status of the other four numbers?

Possible Answers:

, and  are even.

None of the other responses are correct.

 and  are even;  and  are odd.

 and  are odd;  and  are even.

, and  are odd.

Correct answer:

None of the other responses are correct.

Explanation:

A power of an integer takes on the same odd/even status as that integer. Therefore, without knowing the odd/even status of , we do not know that of , and, subsequently, we cannot know that of . As a result, we cannot know the status of any of the other values of the other three variables in the subsequent statements. Therefore, none of the four choices are correct.

Example Question #1 : Even / Odd Numbers

You are given that  are all positive integers. Also, you are given that:

You are given that  is odd, but you are not told whether  is even or odd. What can you tell about whether the values of the other four variables are even or odd?

Possible Answers:

 , and  are odd.

 and  are odd;  is even;  can be either.

 and  are even;  is odd;  can be either.

  and  are odd and  and  are even.

  and  are even and  and  are odd.

Correct answer:

  and  are odd and  and  are even.

Explanation:

, the product of an even integer and another integer, is even. Therefore,  is equal to the sum of an odd number  and an even number , and it is odd.

, the product of odd integers, is odd, so , the sum of odd integers  and , is even.

, the product of an odd integer and an even integer, is even, so , the sum of an odd integer  and even integer , is odd.

, the product of odd integers, is odd, so , the sum of odd integers  and , is even.

The correct response is that  and  are odd and that  and  are even.

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