GMAT Math : Data-Sufficiency Questions

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Example Questions

Example Question #61 : Dsq: Understanding Functions

Let

be a function with the set of all real numbers as its domain, and let the function have an inverse $f^{-1}$ .

What is the -intercept of the graph of $f^{-1}$ ?

Statement 1: f(0) = 6 .

Statement 2: The graphs of and $f^{-1}$ intersect only at the point (4, 4) .

Possible Answers:

STATEMENT 2 ALONE provides sufficient information to answer the question, but STATEMENT 1 ALONE does NOT provide sufficient information to answer the question.

BOTH STATEMENTS TOGETHER do NOT provide sufficient information to answer the question.

BOTH STATEMENTS TOGETHER provide sufficient information to answer the question, but NEITHER STATEMENT ALONE provides sufficient information to answer the question.

STATEMENT 1 ALONE provides sufficient information to answer the question, but STATEMENT 2 ALONE does NOT provide sufficient information to answer the question.

EITHER STATEMENT ALONE provides sufficient information to answer the question.

Correct answer:

BOTH STATEMENTS TOGETHER do NOT provide sufficient information to answer the question.

Explanation:

The -intercept of the graph of $f^{-1}$ is the point (0, b) at which the graph intersects the -axis. At that point, $f^{-1}(0) = b$ , or, equivalently, f(b) = 0 .

Therefore, we need to find the value for which f(b) = 0 .

Between the two statements, we only know that f(0) = 6 and f(4) = 4 . The value of for which f(b) = 0 cannot be determined.

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Example Question #891 : Data Sufficiency Questions

True or false: $\left \{ a_{n} \right \}$ , n = 1, 2, 3,... is an arithmetic sequence.

Statement 1: $a_{1}+ a_{4} \ne a_{2} + a_{3}$

Statement 2: $a_{6}- a_{5} = a_{8} - a_{7}$

Possible Answers:

BOTH STATEMENTS TOGETHER provide sufficient information to answer the question, but NEITHER STATEMENT ALONE provides sufficient information to answer the question.

EITHER STATEMENT ALONE provides sufficient information to answer the question.

STATEMENT 1 ALONE provides sufficient information to answer the question, but STATEMENT 2 ALONE does NOT provide sufficient information to answer the question.

BOTH STATEMENTS TOGETHER do NOT provide sufficient information to answer the question.

STATEMENT 2 ALONE provides sufficient information to answer the question, but STATEMENT 1 ALONE does NOT provide sufficient information to answer the question.

Correct answer:

STATEMENT 1 ALONE provides sufficient information to answer the question, but STATEMENT 2 ALONE does NOT provide sufficient information to answer the question.

Explanation:

An arithmetic sequence is one in which the difference of each term in the sequence and the one preceding is constant.

Assume Statement 1 alone.

$a_{1}+ a_{4} \ne a_{2} + a_{3}$

$a_{1}+ a_{4} - a_{1} - a_{3} \ne a_{2} + a_{3} - a_{1} - a_{3}$

$a_{4} - a_{3} \ne a_{2} - a_{1}$ ,

meaning that at least two such differences are unequal, and proving the sequence is not arithmetic.

Statement 2 alone only proves that two such differences are equal, but says nothing about any of the other (infinitely many) such differences. Therefore, it leaves the question unresolved.

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Example Question #63 : Dsq: Understanding Functions

Define f(x)=4x+A and g(x) =Bx+5 .

Is it true that $f = g^{-1}$ ?

Statement 1: A = -10

Statement 2: $B=\frac{1}{2}$

Possible Answers:

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient to answer the question.

BOTH statements TOGETHER are insufficient to answer the question.

Statement 1 ALONE is sufficient to answer the question, but Statement 2 ALONE is NOT sufficient to answer the question.

EITHER statement ALONE is sufficient to answer the question.

Statement 2 ALONE is sufficient to answer the question, but Statement 1 ALONE is NOT sufficient to answer the question.

Correct answer:

EITHER statement ALONE is sufficient to answer the question.

Explanation:

For $f = g^{-1}$ to be each other's inverse, it must be true that

$(f\circ g)(x) =x$ and $(g\circ f)(x) =x$

We can look at the first condition.

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

$(f\circ g)(x) =f(g(x)) = f(Bx+5)=4(Bx+5)+A=4Bx+20+A= x$

For this to be true, it must hold that:

4B=1

$B=\frac{1}{4}$

and

20+A=0

A = -20

Since both statements violate these conditions, it is impossible for $f = g^{-1}$ , even if you are only given one of them.

The answer is that either statement alone is sufficient to answer the question.

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Example Question #1 : Dsq: Simplifying Algebraic Expressions

Evaluate the expression $(x+y)^{2}-x(x+3y)+xy$

1) x = 3

2) y = 2

Possible Answers:

Statement 1 ALONE is sufficient to answer the question, but Statement 2 ALONE is not sufficient.

Statement 2 ALONE is sufficient to answer the question, but Statement 1 ALONE is not sufficient.

EITHER statement ALONE is sufficient to answer the question.

BOTH statements TOGETHER are insufficient to answer the question.

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient to answer the question.

Correct answer:

Statement 2 ALONE is sufficient to answer the question, but Statement 1 ALONE is not sufficient.

Explanation:

Simplify the expression:

$(x+y)^{2}-x(x+3y)+xy$

$= x^{2}+2xy+y^{2}-x^{2}-3xy+xy$

$= x^{2}-x^{2} +xy+2xy-3xy+y^{2}$

$= y^{2}$

Therefore, we only need to know - If we know y = 2 , we calculate that $(x+y)^{2}-x(x+3y)+xy = y^{2} = 2^{2} = 4$

The answer is that Statement 2 alone is sufficient to answer the question, but Statement 1 is not.

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Example Question #1 : Simplifying Algebraic Expressions

Evaluate: $\frac{(x+y)^{2}-(x-y)^{2}}{x}$

Statement 1: x = 5

Statement 2: y=3

Possible Answers:

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient to answer the question.

EITHER statement ALONE is sufficient to answer the question.

Statement 2 ALONE is sufficient to answer the question, but Statement 1 ALONE is NOT sufficient to answer the question.

BOTH statements TOGETHER are insufficient to answer the question.

Statement 1 ALONE is sufficient to answer the question, but Statement 2 ALONE is NOT sufficient to answer the question.

Correct answer:

Statement 2 ALONE is sufficient to answer the question, but Statement 1 ALONE is NOT sufficient to answer the question.

Explanation:

$\frac{(x+y)^{2}-(x-y)^{2}}{x} = \frac{(x^{2}+2xy+y^{2})-(x^{2}-2xy+y^{2})}{x} = \frac{4xy}{x}= 4y$

Therefore, you only need to know the value of to evaluate this; knowing the value of is neither necessary nor helpful.

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Example Question #1 : Simplifying Algebraic Expressions

Evaluate the expression for positive x,y :

$\frac{4x^{2}}{y^{-4}} \cdot \frac{3x^{2}y^{2}}{8} \cdot \frac{5}{(2x^{2}y^{2})^{2}}$

Statement 1: x = 3

Statement 2: y = 4

Possible Answers:

Statement 2 ALONE is sufficient to answer the question, but Statement 1 ALONE is NOT sufficient to answer the question.

Statement 1 ALONE is sufficient to answer the question, but Statement 2 ALONE is NOT sufficient to answer the question.

BOTH statements TOGETHER are insufficient to answer the question.

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient to answer the question.

EITHER statement ALONE is sufficient to answer the question.

Correct answer:

Statement 2 ALONE is sufficient to answer the question, but Statement 1 ALONE is NOT sufficient to answer the question.

Explanation:

$\frac{4x^{2}}{y^{-4}} \cdot \frac{3x^{2}y^{2}}{8} \cdot \frac{5}{(2x^{2}y^{2})^{2}}$

$= \frac{4x^{2}}{y^{-4}} \cdot \frac{3x^{2}y^{2}}{8} \cdot \frac{5}{2^{2} (x^{2})^{2}(y^{2})^{2}}$

$= \frac{4x^{2}}{y^{-4}} \cdot \frac{3x^{2}y^{2}}{8} \cdot \frac{5}{4 x^{2\cdot 2}y^{2\cdot 2}}$

$= \frac{4x^{2}}{y^{-4}} \cdot \frac{3x^{2}y^{2}}{8} \cdot \frac{5}{4 x^{4}y^{4}}$

$= \frac{4x^{2}\cdot 3x^{2}y^{2}\cdot 5}{y^{-4}\cdot 8\cdot 4 x^{4}y^{4}}$

$= \frac{4 \cdot 3\cdot 5 \cdot x^{2}\cdot x^{2}\cdot y^{2}}{8\cdot 4 \cdot x^{4} \cdot y^{4}\cdot y^{-4}}$

$= \frac{60 \cdot x^{2+2}\cdot y^{2}}{32 \cdot x^{4} \cdot y^{4-4}}$

$= \frac{60 \cdot x^{4}\cdot y^{2}}{32 \cdot x^{4}}$

Cancel the $x^{4}$ from both halves:

$= \frac{60 y^{2}}{32 } = \frac{15 y^{2}}{8 }$

As can be seen by the simplification, it turns out that only the value of , which is given only in Statement 2, affects the value of the expression.

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Example Question #891 : Data Sufficiency Questions

What is the value of x+y ?

(1) 7x=7-7y

(2) 13x+13y=13

Possible Answers:

Statement 2 ALONE is sufficient to answer the question, but the other statement alone is not sufficient

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient.

EACH statement ALONE is sufficient to answer the question.

BOTH statements TOGETHER are not sufficient to answer the question.

Statement 1 ALONE is sufficient to answer the question, but the other statement alone is not sufficient

Correct answer:

EACH statement ALONE is sufficient to answer the question.

Explanation:

(1) Add to both sides to make 7x+7y=7 . Then divide through by 7 to get

x+y=1 . This statement is sufficient.

(2) Divide both sides by 13. The equation becomes x+y=1 . This statement is sufficient.

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Example Question #3 : Simplifying Algebraic Expressions

Is d > e ?

(1.) d = e + 5

(2.) $\frac{d}{6} = e - 2$

Possible Answers:

EACH statement ALONE is sufficient to answer the question.

Statement 2 ALONE is sufficient to answer the question, but the other statement alone is not sufficient.

BOTH statements TOGETHER are not sufficient to answer the question.

Statement 1 ALONE is sufficient to answer the question, but the other statement alone is not sufficient.

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient.

Correct answer:

Statement 1 ALONE is sufficient to answer the question, but the other statement alone is not sufficient.

Explanation:

(1) Since 5 must be added to to make it equal to , it follows that d>e . This statement is sufficient.

(2) Multiply both sides by 6 to obtain d = 6e - 12 . Thus, whether d > e or

d < e depends on the value selected for and . For instance, e = 0 implies

d = -12 , (such that e > d ) but e = 20 implies d = 108 ,

(such that e < d ). Therefore, this statement is insufficient.

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Example Question #1 : Dsq: Simplifying Algebraic Expressions

True or false?

$\frac{(x + y)^{2} - (x - y)^{2} }{y} \geq \frac{(x + y)^{2} + (x - y)^{2} }{x^{2}+y^{2}}$

Statement 1: x = 10

Statement 2: y = 7

Possible Answers:

Statement 2 ALONE is sufficient to answer the question, but Statement 1 ALONE is NOT sufficient to answer the question.

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient to answer the question.

Statement 1 ALONE is sufficient to answer the question, but Statement 2 ALONE is NOT sufficient to answer the question.

EITHER statement ALONE is sufficient to answer the question.

BOTH statements TOGETHER are insufficient to answer the question.

Correct answer:

Statement 1 ALONE is sufficient to answer the question, but Statement 2 ALONE is NOT sufficient to answer the question.

Explanation:

Simplify each expression.

$\frac{(x + y)^{2} - (x - y)^{2} }{y}$

$= \frac{(x^{2}+2xy + y^{2}) - (x^{2}-2xy + y^{2}) }{y}$

$= \frac{4xy }{y} = 4x$

$\frac{(x + y)^{2} + (x - y)^{2} }{x^{2}+y^{2}}$

$= \frac{(x^{2}+2xy + y^{2}) + (x^{2}-2xy + y^{2}) }{x^{2}+y^{2}}$

$= \frac{2x^{2} + 2y^{2}}{x^{2}+y^{2}} = \frac{2 \left ( x^{2} + y^{2} \right ) }{x^{2}+y^{2}} = 2$

The inequality, therefore, is equivalent to

$4x \geq 2$ ,

the truth or falsity of which depends only on the value of

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Example Question #892 : Data Sufficiency Questions

True or false?

$\frac{(x + 4y)^{2} - (x - 4y)^{2} }{y} < \frac{(x + 3y)^{2} - (x - 3y)^{2} }{x}$

Statement 1: x = 7

Statement 2: y = 4

Possible Answers:

BOTH statements TOGETHER are insufficient to answer the question.

Statement 1 ALONE is sufficient to answer the question, but Statement 2 ALONE is NOT sufficient to answer the question.

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient to answer the question.

EITHER statement ALONE is sufficient to answer the question.

Statement 2 ALONE is sufficient to answer the question, but Statement 1 ALONE is NOT sufficient to answer the question.

Correct answer:

BOTH statements TOGETHER are sufficient to answer the question, but NEITHER statement ALONE is sufficient to answer the question.

Explanation:

Simplify both expressions algebraically.

$\frac{(x + 4y)^{2} - (x - 4y)^{2} }{y}$

$=\frac{(x^{2} + 2\cdot x\cdot 4y+ (4y)^{2} ) - (x^{2} - 2\cdot x\cdot 4y+ (4y)^{2} ) }{y}$

$=\frac{(x^{2} + 8 xy+ 16y^{2} ) - (x^{2} -8 xy+ 16y^{2} ) }{y}$

$=\frac{16xy }{y} =16x$

Using similar algebra, you can simplify the other expression:

$\frac{(x + 3y)^{2} - (x - 3y)^{2} }{x} = 12y$

The question, assuming the variables have nonzero values, is equivalent to asking whether 16x<12y is true. Since we need to know the values of both variables to answer this, both statements are necessary and sufficient.

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GMAT Math : Data-Sufficiency Questions

Study concepts, example questions & explanations for GMAT Math

All GMAT Math Resources

Example Questions

Example Question #61 : Dsq: Understanding Functions

Example Question #891 : Data Sufficiency Questions

Example Question #63 : Dsq: Understanding Functions

Example Question #1 : Dsq: Simplifying Algebraic Expressions

Example Question #1 : Simplifying Algebraic Expressions

Example Question #1 : Simplifying Algebraic Expressions

Example Question #891 : Data Sufficiency Questions

Example Question #3 : Simplifying Algebraic Expressions

Example Question #1 : Dsq: Simplifying Algebraic Expressions

Example Question #892 : Data Sufficiency Questions

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