GMAT Math : GMAT Quantitative Reasoning

Study concepts, example questions & explanations for GMAT Math

varsity tutors app store varsity tutors android store

Example Questions

Example Question #4 : Understanding Functions

A sequence begins as follows:

\displaystyle 8, 12, ...

It is formed the same way that the Fibonacci sequence is formed. What are the next two numbers in the sequence?

Possible Answers:

\displaystyle 20, 35

\displaystyle 18, 27

\displaystyle 16, 20

\displaystyle 8, 4

\displaystyle 20, 32

Correct answer:

\displaystyle 20, 32

Explanation:

Each term of the Fibonacci sequence is formed by adding the previous two terms. Therefore, do the same to form this sequence:

\displaystyle 8 + 12= 20

\displaystyle 12+20=32

Example Question #3 : Functions/Series

Give the inverse of \displaystyle f (x) = 5x - 7

Possible Answers:

\displaystyle f^{-1}(x)=- \frac{1}{5}x + \frac{7}{5}

\displaystyle f^{-1}(x)= \frac{1}{5}x +7

\displaystyle f^{-1}(x)= \frac{1}{5}x + \frac{7}{5}

\displaystyle f^{-1}(x)= -\frac{1}{5}x +7

\displaystyle f^{-1}(x)= \frac{1}{5}x - \frac{7}{5}

Correct answer:

\displaystyle f^{-1}(x)= \frac{1}{5}x + \frac{7}{5}

Explanation:

The easiest way to find the inverse of \displaystyle f (x) is to replace \displaystyle f (x) in the definition with \displaystyle y , switch \displaystyle y with \displaystyle x, and solve for \displaystyle y in the new equation.

\displaystyle y = 5x - 7

\displaystyle x = 5y - 7

\displaystyle x + 7 = 5y - 7 + 7

\displaystyle x + 7 = 5y

\displaystyle \frac{1}{5} \cdot\left ( x + 7 \right ) = \frac{1}{5} \cdot 5y

\displaystyle \frac{1}{5} x + \frac{7}{5} = y

\displaystyle f^{-1}(x)= \frac{1}{5}x + \frac{7}{5}

Example Question #4 : Functions/Series

Define \displaystyle f (x) = x^{3} - 8. Give \displaystyle f^{-1} (x)

Possible Answers:

\displaystyle f^{-1}(x) = 2+ \sqrt[3]{x }

\displaystyle f^{-1}(x) = \sqrt[3]{x +2}

\displaystyle f^{-1}(x) = \sqrt[3]{x +8}

\displaystyle f^{-1}(x) = 8+ \sqrt[3]{x }

\displaystyle f^{-1}(x) = 2- \sqrt[3]{x }

Correct answer:

\displaystyle f^{-1}(x) = \sqrt[3]{x +8}

Explanation:

The easiest way to find the inverse of \displaystyle f (x) is to replace \displaystyle f (x) in the definition with \displaystyle y , switch \displaystyle y with \displaystyle x, and solve for \displaystyle y in the new equation.

\displaystyle y = x^{3} - 8

\displaystyle x= y^{3} - 8

\displaystyle x +8= y^{3} - 8 +8

\displaystyle x +8= y^{3}

\displaystyle \sqrt[3]{x +8}= \sqrt[3]{y^{3}}

\displaystyle y = \sqrt[3]{x +8}

Example Question #5 : Functions/Series

Define \displaystyle f(x) = x^{2}- 4 and \displaystyle g(x) = x^{2} + 4.

Give the definition of \displaystyle (f \circ g)(x) .

Possible Answers:

\displaystyle (f \circ g)(x) = x^{4}+8x^{2}+12

\displaystyle (f \circ g)(x) = x^{4}+8x^{2}-12

\displaystyle (f \circ g)(x) = x^{4} -16

\displaystyle (f \circ g)(x) = x^{4} - 8x^{2} +20

\displaystyle (f \circ g)(x) = x^{4}

Correct answer:

\displaystyle (f \circ g)(x) = x^{4}+8x^{2}+12

Explanation:

\displaystyle (f \circ g)(x) = f(g(x))

\displaystyle = f(x^{2}+4)

\displaystyle = (x^{2}+4)^{2}-4

\displaystyle =x^{4} + 8x^{2}+16-4

\displaystyle =x^{4} + 8x^{2}+12

Example Question #1 : Functions/Series

Define \displaystyle g (x) = 5x - 2 .

If \displaystyle g (A) = 11, evaluate \displaystyle A.

Possible Answers:

\displaystyle A=57

\displaystyle A=1.8

\displaystyle A=53

\displaystyle A=2.6

\displaystyle A=4.2

Correct answer:

\displaystyle A=2.6

Explanation:

Solve for \displaystyle A in this equation:

\displaystyle g (A) = 5A - 2 = 11

\displaystyle 5A - 2 + 2 = 11+ 2

\displaystyle 5A = 13

\displaystyle 5A \div 5 = 13\div 5

\displaystyle A = 2.6

Example Question #11 : Functions/Series

Define the operation \displaystyle \Theta as follows:

\displaystyle a \; \Theta \; b = ab + 100

Solve for \displaystyle x : \displaystyle 4\; \Theta \; x = 72

Possible Answers:

\displaystyle x = -9

\displaystyle x = -7

\displaystyle x = -18

\displaystyle x = 9

\displaystyle x = 18

Correct answer:

\displaystyle x = -7

Explanation:

\displaystyle 4\; \Theta \; x = 72

\displaystyle 4x + 100 = 72

\displaystyle 4x + 100 -100 = 72-100

\displaystyle 4x = -28

\displaystyle 4x \div 4 = -28 \div 4

\displaystyle x = -7

Example Question #12 : Functions/Series

Define \displaystyle f(x) = A (x-B)^{3}, where \displaystyle A \neq 0, B \neq 0.

Evaluate \displaystyle f^{-1} (1) in terms of \displaystyle A and \displaystyle B.

Possible Answers:

\displaystyle f^{-1} (1)= B - \frac{1}{\sqrt[3]{A}}

\displaystyle f^{-1} (1)= -B + \frac{1}{\sqrt[3]{A}}

\displaystyle f^{-1} (1)= B + \sqrt[3]{A}

\displaystyle f^{-1} (1)= B + \frac{1}{\sqrt[3]{A}}

\displaystyle f^{-1} (1)= B - \sqrt[3]{A}

Correct answer:

\displaystyle f^{-1} (1)= B + \frac{1}{\sqrt[3]{A}}

Explanation:

This is equivalent to asking for the value of \displaystyle x for which \displaystyle f(x) = 1, so we solve for \displaystyle x in the following equation:

\displaystyle f(x) = 1

\displaystyle A (x-B)^{3} =1

\displaystyle \frac{A (x-B)^{3}}{A} =\frac{1}{A}

\displaystyle (x-B)^{3} =\frac{1}{A}

\displaystyle \sqrt[3]{(x-B)^{3} }=\sqrt[3]{\frac{1}{A}}

\displaystyle x-B =\sqrt[3]{\frac{1}{A}}

\displaystyle x-B = \frac{1}{\sqrt[3]{A}}

\displaystyle x-B + B = B + \frac{1}{\sqrt[3]{A}}

\displaystyle x = B + \frac{1}{\sqrt[3]{A}}

Therefore, \displaystyle f^{-1} (1)= B + \frac{1}{\sqrt[3]{A}}.

Example Question #153 : Algebra

Define an operation \displaystyle \odot as follows:

For any real numbers \displaystyle a,b , 

\displaystyle a \odot b = (a-1) (b-1)

Evaluate \displaystyle \left (5 \odot 5 \right )\odot 5.

Possible Answers:

\displaystyle 96

\displaystyle 64

\displaystyle 60

\displaystyle 75

\displaystyle 100

Correct answer:

\displaystyle 60

Explanation:

\displaystyle \left (5 \odot 5 \right )\odot 5 

\displaystyle = \left [(5 -1) (5 -1) \right ] \odot 5

\displaystyle = (4 \cdot 4 ) \odot 5

\displaystyle = 16 \odot 5

\displaystyle = \left (16-1 \right ) \left (5-1 \right )

\displaystyle = 15 \cdot4 = 60

Example Question #154 : Algebra

An infinite sequence begins as follows:

\displaystyle 1, 2, -3, 4, 5, -6, 7,8,-9 ...

Assuming this pattern continues infinitely, what is the sum of the 1000th, 1001st and 1002nd terms?

Possible Answers:

\displaystyle 1,000

\displaystyle 3

\displaystyle 999

\displaystyle 0

\displaystyle 1,001

Correct answer:

\displaystyle 999

Explanation:

This can be seen as a sequence in which the \displaystyle Nth term is equal to \displaystyle N if \displaystyle N is not divisible by 3, and \displaystyle -N otherwise. Since 1,000 and 1,001 are not multiples of 3, but 1,002 is, the 1000th, 1001st, and 1002nd terms are, respectively,

\displaystyle 1000,1001,-1002

and their sum is 

\displaystyle 1000+ 1001+ \left (-1002 \right ) = 999

Example Question #154 : Algebra

Define \displaystyle f(x) = \sqrt{x} . What is \displaystyle \left (f \circ f \right )(x) ?

Possible Answers:

\displaystyle \left (f \circ f \right )(x) = 2\sqrt{x}

\displaystyle \left (f \circ f \right )(x) = x

\displaystyle \left (f \circ f \right )(x) = x^{2}

\displaystyle \left (f \circ f \right )(x) = \sqrt[4]{x}

\displaystyle \left (f \circ f \right )(x) = \sqrt[3]{x}

Correct answer:

\displaystyle \left (f \circ f \right )(x) = \sqrt[4]{x}

Explanation:

This can best be solved by rewriting \displaystyle \sqrt{ x} as \displaystyle x^{\frac{1}{2}} and using the power of a power property.

\displaystyle \left (f \circ f \right )(x) = f (f(x)) = \left [f(x) \right]^{\frac{1}{2}} =\left ( x^{\frac{1}{2}} \right )^{\frac{1}{2}}=x^{\frac{1}{2}\cdot \frac{1}{2} } =x^{\frac{1}{4} } =\sqrt[4]{x}

Tired of practice problems?

Try live online GMAT prep today.

1-on-1 Tutoring
Live Online Class
1-on-1 + Class
Learning Tools by Varsity Tutors