GMAT 700+ Quant Question 9 | GMAT Geometry DS

The given question is a GMAT 700 level data sufficiency question. We have to determine whether the data given is sufficient to find a unique set of values for the sides of a triangle. If more than one triangle is possible, then the data is not sufficient.

GMAT Data Sufficiency | Directions | Click Here ▼

This data sufficiency problem consists of a question and two statements, labeled (1) and (2), in which certain data are given. You have to decide whether the data given in the statements are sufficient for answering the question. Using the data given in the statements, plus your knowledge of mathematics and everyday facts (such as the number of days in a leap year or the meaning of the word counterclockwise), you must indicate whether -

1. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient to answer the question asked.
2. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient to answer the question asked.
3. BOTH statements (1) and (2) TOGETHER are sufficient to answer the question asked, but NEITHER statement ALONE is sufficient to answer the question asked.
4. EACH statement ALONE is sufficient to answer the question asked.
5. Statements (1) and (2) TOGETHER are NOT sufficient to answer the question asked, and additional data specific to the problem are needed.

Numbers

All numbers used are real numbers.

Figures

A figure accompanying a data sufficiency question will conform to the information given in the question but will not necessarily conform to the additional information given in statements (1) and (2)

Lines shown as straight can be assumed to be straight and lines that appear jagged can also be assumed to be straight

You may assume that the positions of points, angles, regions, etc. exist in the order shown and that angle measures are greater than zero.

All figures lie in a plane unless otherwise indicated.

Note

In data sufficiency problems that ask for the value of a quantity, the data given in the statement are sufficient only when it is possible to determine exactly one numerical value for the quantity.

Question 9: a, b, and c are sides of a right triangle. What is the area of the triangle?

Statement 1: a = 4.
Statement 2: a + b + c = 12.

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Video Explanation

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Explanatory Answer | GMAT Triangles DS

Step 1: Decode Question Stem and Get Clarity

Q1. When is the data sufficient?
If we are able to get a UNIQUE value for the area of the triangle from the information given in the statements, the data is sufficient.

Q2. What should you watch out for?
1. Check to see whether more than one set of values are possible with the given data. For e.g., more than one right triangle can be described for a given hypotenuse of 10 units.
2. Remember that sides of a triangle need not necessarily be integers. Particularly, one might be tempted to think that only triangles whose sides are Pythagorean triplets are right triangles. All Pythagorean triplets are right triangles. But all right triangles need not be Pythagorean triplets. For instance 1, 1, √2 will form sides of a right triangle, where one of the sides is not an integer.

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Step 2: Evaluate Statement 1 ALONE

Statement 1: a = 4

It is not possible to find the area of a right triangle with information about just one of its sides and no other information about the triangle.

We are not able to find the area using statement 1.
Hence, statement 1 is not sufficient.
Eliminate answer option A and D.

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Step 3: Evaluate Statement 2 ALONE

Statement 2: a + b + c = 12

The temptation is to conclude that the sides are 3, 4, and 5. These values will form sides of a right triangle and the sum of a, b, and c is 12.

But before concluding that we have a definite answer, let us check whether any right triangle other than 3, 4, and 5 is possible.

For instance, it is possible to have a right isosceles triangle whose perimeter is 12.
The area of that triangle will be different from that of the triangle with sides 3, 4, and 5.

We are not able to find a UNIQUE area using statement 2.
Hence, statement 2 is not sufficient.
Eliminate answer option B.

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Step 4: Evaluate Statements TOGETHER

Statements: a = 4 & a + b + c = 12

In a right triangle, the longest side is the hypotenuse.
Side that measures 4 is therefore, not the hypotenuse as 4 is the average of the 3 sides.
The hypotenuse has to necessarily be greater than the average of the 3 sides.
So, either b or c is the hypotenuse.

Let us assume c to be the hypotenuse. So, 4 and b are the two perpendicular sides of the right triangle.
4 + b + c = 12. So, b + c = 8. Therefore, b = 8 - c

Applying Pythagoras Theorem, c² = 4² + (8 - c)²
Solving for c, c² = 16 + 64 - 16c + c²
16c = 80. So, c = 5.
If c = 5, b = 8 - c = 3
Using the two statements, we could get a unique set of values for a, b, and c.
Hence, we will be able to find the area of the triangle.

Statements together are sufficient to find a UNIQUE value as the area of the right triangle.
Eliminate answer option E.

Choice C is the correct answer.