GMAT Math : GMAT Quantitative Reasoning

Study concepts, example questions & explanations for GMAT Math

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Example Questions

Example Question #9 : Dsq: Calculating The Height Of An Equilateral Triangle

Given  and , with  an equilateral triangle. Construct the altitude from  to  on , and the altitude from  to  on .

Which, if either, of   and  is longer? 

Statement 1: 

Statement 2:  is a right angle.

Possible Answers:

EITHER 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.

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.

BOTH statements TOGETHER are insufficient 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:

Assume both statements are true. From Statement 1 alone,  , and , so  and . Therefore, between  and , two pairs of corresponding sides are congruent. 

 is an equilateral triangle, so ; from Statement 2,  is a right angle, so . This means that the included angle in  is of greater measure, so by the Side-Angle-Side Inequality Theorem, or Hinge Theorem, it has the longer opposite side, or . Both triangles are isosceles, so both altitudes divide the triangles into congruent right triangles, and by congruence,  and  are the midpoints of their respective sides. This means that 

By the Pythagorean Theorem,

 

and 

Since  and ,

meaning that  is the longer altitude.

Note that this depended on knowing both statements to be true. Statement 1 alone is insufficient, since, for example, had  measured less than , then by the same reasoning,  would have been the shorter altitude. Statement 2 alone is insufficient because it gives information only about one angle, and nothing about any side lengths.

Example Question #10 : Dsq: Calculating The Height Of An Equilateral Triangle

Given equilateral triangles  and , construct the altitude from  to  on , and the altitude from  to  on .

True or false:  or  have the same length.

Statement 1:  and  are chords of the same circle.

Statement 2:   and  have the same area.

Possible Answers:

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.

Statement 2 ALONE is sufficient to answer the question, but Statement 1 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:

Statement 1 alone is inconclusive, since chords of the same circle can have different lengths.

Statement 2 alone is conclusive. The common side length  of an equilateral triangle depends solely on the area, so it follows that the sides of two triangles of equal area will have the same common side length. Also, each altitude divides its triangle into two 30-60-90 triangles. Examining  and , we can easily find that these triangles are congruent by way of the Angle-Side-Angle. Postulate, so it follows by triangle congruence that .

Example Question #331 : Geometry

Given equilateral triangles  and , construct the altitude from  to  on , and the altitude from  to  on .

Which, if either, of   and  is longer? 

Statement 1: 

Statement 2: 

Possible Answers:

BOTH statements TOGETHER are insufficient to answer the question. 

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

Explanation:

Let  and  be the common side lengths of   and . The length of an altitude of a triangle is solely a function of its side length, so it follows that the triangle with the greater side length is the one whose altitude is the longer. Therefore, the question is equivalent to which, if either, of  or  is the greater.

Assume Statement 1 alone. This statement can be rewritten as

It follows that  has the greater side length, and, consequently, that its altitude  is longer than .

Assume Statement 2 alone.  divides the triangle into two congruent triangles, so  is the midpoint of ; therefore, . Statement 2 can be rewritten as

This statement is inconclusive. Suppose —that is, each side of  is of length 1. Then , and  all make that inequality true; without further information, it is therefore unclear whether , the side length of , is less than, equal to, or greater than , the side length of . Consequently, it is not clear which triangle has the longer altitude.

Example Question #331 : Geometry

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What is the perimeter of

(1) The area of the triangle is .

(2)  is an equilateral triangle.

Possible Answers:

Each statement alone is sufficient

Statement 2 alone is sufficient

Statement 1 alone is sufficient

Statements 1 and 2 taken together are not sufficient

Both statements together are sufficient

Correct answer:

Both statements together are sufficient

Explanation:

To find the perimeter we should be able to calculate each sides of the triangle.

Statement 1 tells us the area of the triangle. From this we can't calculate anything else, since we don't know whether the triangle is of a special type.

Statement 2 tells us that the triangle is equilateral. Again This information alone is not sufficient.

Taken together these statements allow us to find the sides of the equilateral triangle ABC. Indeed, the area of an equilateral triangle is given by the following formula: . Where  is the area and  the length of the side.

Therefore both statements are sufficient.

Example Question #2 : Dsq: Calculating The Perimeter Of An Equilateral Triangle

Find the perimeter of  given the following:

I) .

II) Side .

Possible Answers:

Both statements are needed to answer the question.

Neither statement is sufficient to answer the question. More information is needed.

Either statement is sufficient to answer the question.

Statement I is sufficient to answer the question, but statement II is not sufficient to answer the question.

Statement II is sufficient to answer the question, but statement I is not sufficient to answer the question.

Correct answer:

Both statements are needed to answer the question.

Explanation:

To find perimeter, we need the side lengths.

I) Gives us the measure of two angles. The given measurement is equal to 60 degrees. This means the last angle is also 60 degrees.

II) Gives us one side length, but because we know from I) that this is an equilateral triangle, we know that all the sides have the same length. 

Add up all the sides to get the perimeter.

We need I) and II) to find the perimeter

Example Question #1 : Dsq: Calculating The Perimeter Of An Equilateral Triangle

Given two equilateral triangles  and , which, if either, has the greater perimeter?

Statement 1: 

Statement 2: 

Possible Answers:

EITHER statement ALONE is sufficient to answer the question.

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 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.

Correct answer:

EITHER statement ALONE is sufficient to answer the question.

Explanation:

The area of an equilateral triangle is given by the formula

,

where  is its common sidelength. It follows that the triangle with the greater sidelength has the greater area.

We will let  and  stand for the common sidelength of  and , respectively. The question becomes which, if either, of  and  is the greater.

Statement 1 alone can be rewritten by multiplying:

Therefore, .

Therefore, , the length of one side of  is less than , the length of one side of .

Statement 2 alone can be rewritten as . Again, it follows that .

From either statement alone, it follows that  has the greater sidelength, and, consequently, the greater area.

Example Question #451 : Data Sufficiency Questions

Given two equilateral triangles  and , which, if either, has the greater perimeter?

Statement 1: 

Statement 2:  has greater area than .

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:

EITHER statement ALONE is sufficient to answer the question.

Explanation:

Since an equilateral triangle has three sides of equal measure, the perimeter of an equilateral triangle is three times its sidelength, so the triangle with the greater common sidelength has the greater perimeter.

Statement 1 gives precisely this information; since one side of  is longer than one side of , it follows that  has the longer perimeter.

Statement 2 gives that  has the greater area. Since the area of an equilateral triangle depends only on the common length of its sides, the triangle with the greater area, , must also have the greater sidelength and, consequently, the greater perimeter.

Example Question #5 : Dsq: Calculating The Perimeter Of An Equilateral Triangle

Give the perimeter of equilateral triangle .

Statement 1:  is a radius of a circle with area .

Statement 2:  is the hypotenuse of a 30-60-90 triangle with area .

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.

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

EITHER statement ALONE is sufficient to answer the question.

Correct answer:

EITHER statement ALONE is sufficient to answer the question.

Explanation:

Assume Statement 1 alone. To find the radius of a circle with area , use the area formula:

This is also the length of each side of , so its perimeter is three times this, or 24.

Assume Statement 2 alone. If we let  be the length of , then, since this the hypotenuse of a 30-60-90 triangle, by the 30-60-90 Theorem, the legs measure  and . Half the product of their lengths is equal to area , so

.

As before, the sidelength of  is 8 and the perimeter is 24.

Example Question #92 : Triangles

Given two equilateral triangles  and , which has the greater perimeter?

Statement 1:  is the midpoint of .

Statement 2:  is the midpoint of .

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.

BOTH statements TOGETHER are insufficient to answer the question. 

EITHER 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.

Correct answer:

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

Explanation:

Neither statement alone is enough to determine which triangle has the greater perimeter, as each statement gives information about only one point. 

Assume both statements to be true. Since  is the segment that connects the endpoints of two sides of , it is a midsegment of the triangle, whose length is half the length of the side of  to which it is parallel. Therefore, the sidelength of  is half that of , and their perimeters are similarly related. This makes  the triangle with the greater perimeter.

Example Question #7 : Dsq: Calculating The Perimeter Of An Equilateral Triangle

Which, if either, of equilateral triangles  and , has the greater perimeter?

Statement 1: 

Statement 2: 

Possible Answers:

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. 

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.

EITHER statement ALONE is sufficient to answer the question.

Correct answer:

EITHER statement ALONE is sufficient to answer the question.

Explanation:

Since the perimeter of an equilateral triangle is three times its common sidelength, comparison of the lengths of the sides is all that is necessary to determine which triangle, has the greater perimeter.

If we let  and  be the common sidelengths of  and , respectively, Statement 1 can be rewritten as the equation . This can be expressed as follows:

Therefore, .

Statement 2 can be rewritten as 

Once again,

Since either statement alone establishes that , it follows that  has the longer sides and, consequently, the greater perimeter of the triangles.

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