SAT Math : SAT Mathematics

Study concepts, example questions & explanations for SAT Math

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Example Questions

Example Question #13 : Prime Numbers

Which is prime?

Possible Answers:

Correct answer:

Explanation:

This will require us to know the divisibility rule of . The reason for this choice is that some of the numbers are palindromes like  so we eliminate . For the three digit numbers, the divisibility rule for  is add the outside digits and if the sum matches the sum then it is divisible. Let's see.

Based on this test,  is not divisible by  and is our answer.

Example Question #1631 : Sat Mathematics

If p is a prime number, what could also be prime?

Possible Answers:

3p

p^{2}

2p

p-2

Correct answer:

p-2

Explanation:

Plug in a prime number such as  and evaluate all the possible solutions. Note that the question asks which value COULD be prime, not which MUST BE prime. As soon as your number-picking yields a prime number, you have satisfied the "could be prime" standard and know that you have a correct answer.

Example Question #1 : How To Factor A Number

If x is the greatest prime factor of 42, and y is the greatest prime factor of 55, what is the value of xy?

Possible Answers:

105

10

15

77

21

Correct answer:

77

Explanation:

Find the prime factors of 42: 7, 3, 2

Find the prime factors of 55: 5, 11

Product of the greatest factors: 7 and 11 = 77

Example Question #291 : Arithmetic

If p is a prime number greater than 1, how many positive factors does p4 have?

Possible Answers:

Six

Four

Two

Three

Five

Correct answer:

Five

Explanation:

3 is a prime number that is easy to work with, so we can plug that in for p. p4 = 81. The positive factors of 81 are 1, 3, 9, 27, and 81. Thus, the answer is five factors.

Let's look at another prime number to plug in for p. If we plug in 2, another easy prime number to work woth, we get p4 = 16. The positive factors of 16 are 1, 2, 4, 8 and 16.

Notice that when p = prime number greater than 1, the positive factors for p4 are 1, p, p2, p3 and p4. Multiplying pn by p only adds pn as a factor when p is prime, so you will have n factors plus 1 which is a factor, so p4 has 5 factors.

 

Example Question #294 : Arithmetic

What is the sum of all prime factors of 152?

Possible Answers:

25

6

21

9

Correct answer:

25

Explanation:

Since 152 is divisible by 2, start by dividing 152 by 2 which gives you factors of 2 and 76. 2 is a prime factor (cannot be divisible by anything other than itself and 1) but 76 can still be divided by 2. Continue dividing until there are only prime factors. You should get prime factors of 2, 2, 2, and 19. 2+2+2+19 = 25.

Example Question #1 : Other Factors / Multiples

Let x, y, and z be three distinct positive integers. Which of the following values of y is possible,

if x3y2z = 1000

Possible Answers:

5

10

2,10

2,5

2

Correct answer:

2,5

Explanation:

If y = 2, then x3z = 250. This means that x could be equal to 1, and z could be equal to 250. This would make x, y, and z distinct positive integers. Thus, it is possible for y to equal 2.

If y = 5, then x3z = 40. This means x could be 1, and z could be 40. This would make x, y, and z distinct positive integers.  Therefore, y can equal 5.

If y = 10, then x3z = 10. This means that the only value that x could be is 1. If x were equal to 2, for example, then z would be equal to 10/8, which is not an integer. The same would be true if x were equal to anything other than 1. Thus, x must equal 1, and z must equal 10. However, because y and z must be distinct, y cannot equal 10. 

Thus, y could equal only 2 and 5. 

Example Question #291 : Arithmetic

The product of three consecutive positive integers is 210. What is the sum of the integers?

Possible Answers:
30
21
9
6
18
Correct answer: 18
Explanation:

Let x be the first integer. The next two integers would then be x+1 and x+2. We must find x such that:

x(x+1)(x+2) = 210.

To do this, we need to look at the factors of 210, and find a set of three factors that are also consecutive integers. First, let's find the prime factorization of 210, because then we can use that to determine all of the possible factors of 210.

210 = 10 x 21 = 2 x 5 x 21 = 2 x 5 x 3 x 7

Thus, the prime factorization of 210 is 2 x 3 x 5 x 7.

We can notice now that 5 and 7 are almost consecutive integers, and the only number missing between them is 6. If we multiply 2 and 3, we get 6. Thus 210 can be written as 5 x 6 x 7. This means that the consecutive integers are 5, 6, and 7, and their sum is 18.

Example Question #292 : Arithmetic

If the variable x is an integer divisible by the numbers 2 and 3, which of the following is necessarily divisible by 2, 3 and 5?

Possible Answers:

5x + 2

6x + 30

5x + 30

x + 30

2x + 30

Correct answer:

5x + 30

Explanation:

For this question, use the fact that a sum of two multiples is a multiple. In other words:

if x is a multiple of 3 and y is a multiple of 3: (x + y) is a multiple of 3.

Thus in this question, x is a multiple of 2 and 3. We need to find a number that is a multiple of 2, 3, and 5. 

Take 5x + 30:

[x is divisible by 2. 5 times x is still divisble by 3. 30 is divisible by 2.] -> divisible by 2.

[x is divisible by 3. 5 times x is still divisble by 3. 30 is divisible by 3.] -> divisible by 3.

[5x is divisible by 5. 30 is divisible by 5.] -> divisible by 5.

Thus 5x + 30 is divisible by 2, 3 and 5.

Example Question #298 : Arithmetic

If xy = 100 and x and y are distinct positive integers, what is the smallest possible value of xy?

Possible Answers:

101

20

52

25

29

Correct answer:

25

Explanation:

Consider the possible values for (xy):

(1, 100)

(2, 50)

(4, 25)

(5, 20)

Note that (10, 10) is not possible since the two variables are to be distinct. The sums of the above pairs, respectively, are:

1 + 100 = 101

2 + 50 = 52

4 + 25 = 29

5 + 20 = 25, the smallest possible value.

Example Question #1 : Other Factors / Multiples

If p is an integer, then which of the following could be equal to (6 + 2p)(3)

Possible Answers:

75

81

70

68

84

Correct answer:

84

Explanation:

Let n represent all of the numbers that are equal to (6 + 2p)(3). Then, let's solve for p in terms of n.

(6 + 2p)(3) = n

Divide both sides by 3.

(6 + 2p) = n/3

Subtract six from both sides.

2p = –6 + n/3

Divide both sides by 2.

p = –3 + n/6

Since we are told that p is an integer, the only way that p can be an integer is if n is a multiple of 6. Only a multiple of six, when divided by six, will yield an integer number. Any integer plus –3 will also be an integer, since the sum of two integers is always an integer.

In short, we must look for the answer choice that is a multiple of 6. Of the choices, only 84 is a multiple of 6.

The answer is 84. 

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