GMAT Math : DSQ: Calculating the area of an equilateral triangle

Study concepts, example questions & explanations for GMAT Math

varsity tutors app store varsity tutors android store

Example Questions

2 Next →

Example Question #21 : Equilateral Triangles

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

Statement 1: 

Statement 2: 

Possible Answers:

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.

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. 

Correct answer:

EITHER statement ALONE is sufficient to answer the question.

Explanation:

Since the area of an equilateral triangle is solely dependent on the length of one side, it follows that the triangle with the greater sidelength has the greater area.

Statement 1 alone gives that the length of one side of  is greater than that on one side of .It follows that  has the greater area.

Statement 2 alone gives that , from which it follows that

and 

.

Again, this shows that  has the greater sidelength and the greater area.

Example Question #22 : Equilateral Triangles

Give the area of equilateral triangle .

Statement 1:  is a diameter of a circle with circumference .

Statement 2:  is a side of a 45-45-90 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:

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

Explanation:

Assume Statement 1 alone. To find the diameter of a circle with circumference , divide the circumference by  to get . This is also the length of each side of the triangle, so we can get the area using the area formula:

.

Assume Statement 2 alone. A 45-45-90 Triangle has congruent legs, and the area is half the product of their lengths, so if we let  be the common sidelength,

By the 45-45-90 Theorem, the hypotenuse has length  times this, or .

Since it is not given whether  is a leg or the hypotenuse of a right triangle, however, the length of  - and consequently, the area - is not clear.

Example Question #23 : Equilateral Triangles

Find the area of an equilateral triangle.

  1. A side measures .
  2. An angle measures .
Possible Answers:

Both statements taken together are sufficient to answer the question, but neither statement alone is sufficient.

Each statement alone is sufficient to answer the question.

Statements 1 and 2 are not sufficient, and additional data is needed to answer the question.

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

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

Correct answer:

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

Explanation:

In an equilateral triangle all sides are of the same length and all internal angles measure to 

Statement 1: 

Where  represents the length of the side.

If we're given the side, we can calculate the area:

Statement 2: We don't need the angle to find the area.

2 Next →

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