PSAT Math : Arithmetic

Study concepts, example questions & explanations for PSAT Math

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Example Questions

Example Question #1 : How To Find Consecutive Integers

Four consecutive integers have a mean of 9.5. What is the largest of these integers?

Possible Answers:

9

13

12

8

11

Correct answer:

11

Explanation:

Four consecutive integers could be represented as n, n+1, n+2, n+3

Therefore, by saying that they have a mean of 9.5, we mean to say:

(n + n+1 + n+2 + n+ 3)/4 = 9.5

(4n + 6)/4 = 9.5 → 4n + 6 = 38 → 4n = 32 → n = 8

Therefore, the largest value is n + 3, or 11.

Example Question #1 : Consecutive Integers

The sum of four consecutive odd integers is equal to 96. How many of the integers are prime?

Possible Answers:

4

1

3

0

2

Correct answer:

1

Explanation:

Let x be the smallest of the four integers. We are told that the integers are consecutive odd integers. Because odd integers are separated by two, each consecutive odd integer is two larger than the one before it. Thus, we can let + 2 represent the second integer, + 4 represent the third, and + 6 represent the fourth. The sum of the four integers equals 96, so we can write the following equation:

x + (+ 2) + (+ 4) + (+ 6) = 96

Combine x terms.

4x + 2 + 4 + 6 = 96

Combine constants on the left side.

4x + 12 = 96

Subtract 12 from both sides.

4x = 84

Divide both sides by 4.

x = 21

This means the smallest integer is 21. The other integers are therefore 23, 25, and 27.

The question asks us how many of the four integers are prime. A prime number is divisible only by itself and one. Among the four integers, only 23 is prime. The number 21 is divisible by 3 and 7; the number 25 is divisible by 5; and 27 is divisible by 3 and 9. Thus, 23 is the only number from the integers that is prime. There is only one prime integer.

The answer is 1. 

Example Question #1651 : Sat Mathematics

The sum of three consecutive integers is 60. Find the smallest of these three integers.

Possible Answers:

18

22

19

20

21

Correct answer:

19

Explanation:

Assume the three consecutive integers equal x, x + 1, and x + 2. The sum of these three integers is 60. Thus,

x + x + 1 + x + 2 = 60

3x + 3 = 60

3x = 57

x = 19

Example Question #2 : How To Find Consecutive Integers

Possible Answers:

Correct answer:

Explanation:

Example Question #2 : How To Find Consecutive Integers

In the repeating pattern 9,5,6,2,1,9,5,6,2,1......What is the 457th number in the sequence?

 

Possible Answers:

5

1

2

1

9

Correct answer:

5

Explanation:

There are 5 numbers in the sequnce.

How many numbers are left over if you divide 5 into 457?

There would be 2 numbers!

The second number in the sequence is 9,5,6,2,1

Example Question #1 : Consecutive Integers

If  are consecutive, non-negative integers, how many different values of  are there such that  is a prime number?

Possible Answers:

Correct answer:

Explanation:

Since  are consecutive integers, we know that at least 2 of them will be even. Since we have 2 that are going to be even, we know that when we divide the product by 2 we will still have an even number.  Since 2 is the only prime that is even, we must have:

What we notice, however, is that for , we have the product is 0.  For , we have the product is 24.  We will then never have a product of 4, meaning that is never going to be a prime number.

Example Question #1652 : Sat Mathematics

Four consecutive odd integers have a sum of 32. What are the integers?

Possible Answers:

Correct answer:

Explanation:

Consecutive odd integers can be represented as x, x+2, x+4, and x+6.

We know that the sum of these integers is 32. We can add the terms together and set it equal to 32:

x + (x+2) + (x+4) + (x+6) = 32

4x + 12 = 32

4x = 20

x = 5; x+2=7; x+4 = 9; x+6 = 11

Our integers are 5, 7, 9, and 11.

Example Question #1 : Common Difference In Sequences

How many integers in the following infinite series are positive: 100, 91, 82, 73 . . . ?

Possible Answers:

13

11

9

12

10

Correct answer:

12

Explanation:

The difference between each number in the series is 9. You can substract nine 11 times from 100 to get 1: 100 – 9x11 = 1. Counting 100, there are 12 positive numbers in the series.

Example Question #11 : Sequences

In a sequence of numbers, each term is  times larger than the one before it. If the 3rd term of the sequence is 12, and the 6th term is 96, what is the sum of all of the terms less than 250?

Possible Answers:

384

381

372

378

192

Correct answer:

381

Explanation:

Let's call the first term in the sequence a1 and the nth term an

We are told that each term is r times larger than the one before it. Thus, we can find the next term in the sequence by multiplying by r. 

a1 = a1

a2 = r(a1)

a3 = r(a2) = r(r(a1)) = r2(a1)

a4 = r(a3) = r(r2(a1)) = r3(a1)

an = r(n–1)a1

We can use this information to find r.  

The problem gives us the value of the third and the sixth terms. 

a3 = r2(a1) = 12

a6 = r5(a1) = 96

Let's solve for a1 in terms of r and a3

a1 = 12/(r2)

Let's then solve for a1 in terms of r and a6.

a1 = 96/(r5)

Now, we can set both values equal and solve for r.

12/(r2) = 96/(r5)

Multiply both sides by r5 to get rid of the fraction.

12r5/r2 = 96

Apply the property of exponents which states that ab/ac = ab–c.

12r3 = 96

Divide by 12 on both sides.

r3 = 8

Take the cube root of both sides.

r = 2

This means that each term is two times larger than the one before it, or that each term is one half as large as the one after it. 

a2 must equal a3 divided by 2, which equals 12/2 = 6.

a1 must equal a2 divided by 2, which equals 6/2 = 3.

Here are the first eight terms of the sequence:

3, 6, 12, 24, 48, 96, 192, 384

The question asks us to find the sum of all the terms less than 250. Only the first seven terms are less than 250. Thus the sum is equal to the following:

sum = 3 + 6 + 12 + 24 + 48 + 96 + 192 = 381

 

Example Question #361 : Arithmetic

The first term of an arithmetic sequence is 20; the tenth term is 100. What is the sixteenth term?

Possible Answers:

Correct answer:

Explanation:

Given terms  of an arithmetic sequence, , the common difference  is 

Setting , the common difference is found to be

The  term of the sequence  is 

Setting , this term is found to be

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