GMAT Math : Geometry

Study concepts, example questions & explanations for GMAT Math

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Example Questions

Example Question #212 : Data Sufficiency Questions

Find the diagonal of a square.

Statement 1:  The perimeter of the square is known.

Statement 2:  A secondary square with a known area encloses the primary square where all 4 corners of the primary square touch each of secondary square's edges.

Possible Answers:

Correct answer:

Explanation:

Statement 1:  The perimeter of the square is known.

A square has four equal sides.  Write the perimeter formula for squares.

The side length of a square is a fourth of the perimeter.

Statement 2:  A secondary square with a known area encloses the primary square where all 4 corners of the primary square touch each of secondary square's edges.

If the primary square corners touch each of the secondary square edges, they must touch at the midpoint of each edge.  Since Statement 2 mentions that the secondary square area is known, it is possible to solve for the edge length and the diagonal of the secondary square.  Write the formula for the area of a square.

The diagonal of the secondary square can be solved by using the Pythagorean Theorem.

The side length of the secondary square also must equal the diagonal of the primary square.

Therefore:

Example Question #52 : Quadrilaterals

Parallelogram

What are the lengths of the diagonals in the parallelogram ?

1) 

2) 

Possible Answers:

Statement 1 alone is sufficient.

Either of the statements alone is sufficient.

Statement 2 alone is sufficient.

Together, the two statements are sufficient.

Neither of the statements, separate or together, is sufficient.

Correct answer:

Together, the two statements are sufficient.

Explanation:

Each of the statements, 1 and 2, provide something integral to calculating the length of a diagonal: an angle and the length of the sides connected to its vertex. The diagonal would be the third leg of the resulting triangle, and can be calculated using the law of cosines:

Since this is a parellelogram, knowing one angle allows us to know all the angles.

Example Question #101 : Geometry

Parallelogram

For the parellogram , the longest diagonal is . Is ?

1) The area of  is 

2) The perimeter of  is 

Possible Answers:

Together, the two statements are sufficient.

Statement 2 alone is sufficient.

Statement 1 alone is sufficient.

Either of the statements is sufficient.

Neither of the statements, separate or together, is sufficient.

Correct answer:

Statement 2 alone is sufficient.

Explanation:

Area alone is not enough information. Imagine, for instance, a parallelogram with a shorter side of  and a longer side of . The diagonal would be well above 

However, with the perimeter, the smaller and larger sides must add up to one half of it, .

The longer diagonal reaches its maximum with the larger internal angle widens towards  degrees, and the parallelogram flattens into a line. Using the law of cosines, this translates to:

.

At its max, the diagonal could be no greater than 

Example Question #101 : Geometry

Ronald is making a bookshelf with a rectangular base that will be two yards tall. What is the area of the base?

I) The distance around the base will be  yards.

II) The smaller sides of the base are half the length of the longer sides.

Possible Answers:

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

Either statement alone is sufficient to answer the question.

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

Both statements together are needed 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 together are needed to answer the question.

Explanation:

To find the area we need the length and width of the rectangle. We can use II together with I to make an equation for perimeter with only one unknown.

So we need both to solve.

Solve for  and then go back to find  and then with that you can find the area of the base and you are finished.

Example Question #103 : Geometry

Find a possible width of rectangle .

I)  has a perimeter of  fathoms.

II)  has a diagonal length of  fathoms.

Possible Answers:

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

Either statement is sufficient to answer the question.

Both statements are needed to answer the question.

 

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

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

Correct answer:

Both statements are needed to answer the question.

 

Explanation:

When asked to find the width of a rectangle we will need to use both statemests together.

For Statement I) we can use the perimeter formula.

Now, for Statement II) we will use the length of the diagonal along with the Pythagorean Theorem.

From here you can solve the perimeter equation in terms of either l or w. Then you can use substitution into the Pythagorean Theorem to solve for a possible width. 

Example Question #102 : Geometry

Find the length of the side of a rectangle with a width three times the length.

  1. The area of the rectangle is .
  2. The perimeter of the rectangle is 
Possible Answers:

Each statement alone is sufficient to answer the question.

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

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

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

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

Correct answer:

Each statement alone is sufficient to answer the question.

Explanation:

Statement 1: 

Statement 1 is sufficient to answer the question

Statement 2: 

Statement 2 is also sufficient to answer the question

Example Question #1 : Rectangles

A rectangle has a width measuring twice the length. Find the length.

  1. The rectangle has a perimeter of .
  2. The rectangle's area is .
Possible Answers:

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.

Each statement alone is sufficient to answer the question.

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

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

Correct answer:

Each statement alone is sufficient to answer the question.

Explanation:

Statement 1:      

Recall the formula to find the perimeter of a rectangle. Substitute in the given information and solve.

Statement 2: 

Recall the formula for the area of a rectangle. Substitute in the given information and solve.

 

Each statement alone is sufficient to answer the question.

Example Question #3 : Rectangles

Given parallelogram  with diagonal  . Is this parallelogram a rectangle?

1) 

2) 

Possible Answers:

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.

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. 

EITHER statement ALONE is 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:

The length of one diagonal alone does not prove the parallelogram to be a rectangle, nor do the lengths of the sides.

Suppose we know all of these lengths, though. Since  is a parallelogram, if , then 

The sides  and diagonal   form a triangle  with sidelengths 25, 60, and 65. The parallelogram is a rectangle if and only if  is a right angle; therefore, we must determine whether the conditions of the Pythagorean Theorem hold:

This is true;  is a right angle and  is a rectangle.

Therefore, both statements together are sufficient to answer the question, but neither statement alone is sufficient to answer the question.

Example Question #103 : Geometry

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What is the length of the diagonal of rectangle

(1) 

(2)  and 

Possible Answers:

Statements 1 and 2 together are not sufficient

Both statements together are sufficient

Statement 1 alone is sufficient

Statement 2 alone is sufficient

Each statement alone is sufficient

Correct answer:

Statement 2 alone is sufficient

Explanation:

In order to find the diagonal, we must know the sides of the rectangle or know whether the triangles ADC or ABD have special angles.

Statement 1 alone doesn't let us calculate the hypothenuse of the triangles, because we only know one side.

Statement 2 alone is sufficient because it allows us to find all angles of the triangles inside of the rectangle. We can see that they are special triangles with angles 30-60-90. Any triangle with these angles will have its sides in ratio , where  is a constant. Here, , knowing this, we can calculate the length of the hypothenuse, also the diagonal, which will be .

 

Hence, statement 2 is sufficient.

Example Question #104 : Geometry

Rectangle  has a perimeter of , what is its area?

I) The diagonal of  is  inches.

II) The length of one side is  inches.

Possible Answers:

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

Both statements together are needed to answer the question.

Either statement alone is sufficient to answer the question.

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

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

Correct answer:

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

Explanation:

I) Gives us the length of ASOF's diagonal. This by itself does not give us any way of finding the other sides.

II) Gives us one side length. From there we can use the perimeter to find the other side length and then the area.

Therefore, Statement II is sufficient to answer the question.

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