# ISEE Upper Level Quantitative : How to find the volume of a pyramid

## Example Questions

### Example Question #1 : How To Find The Volume Of A Pyramid

Pyramid 1 has a square base with sidelength ; its height is .

Pyramid 2 has a square base with sidelength ; its height is .

Which is the greater quantity?

(a) The volume of Pyramid 1

(b) The volume of Pyramid 2

Possible Answers:

It is impossible to tell from the information given.

(a) and (b) are equal.

(b) is greater.

(a) is greater.

Correct answer:

(b) is greater.

Explanation:

Use the formula on each pyramid.

(a)

(b)

Regardless of , (b) is the greater quantity.

### Example Question #2 : How To Find The Volume Of A Pyramid

Which is the greater quantity?

(a) The volume of a pyramid with height 4, the base of which has sidelength 1

(b) The volume of a pyramid with height 1, the base of which has sidelength 2

Possible Answers:

(a) and (b) are equal.

(b) is greater.

(a) is greater.

It is impossible to tell from the information given.

Correct answer:

(a) and (b) are equal.

Explanation:

The volume of a pyramid with height  and a square base with sidelength  is

.

(a) Substitute

(b) Substitute

The two pyramids have equal volume.

### Example Question #8 : Solid Geometry

Which is the greater quantity?

(a) The volume of a pyramid whose base is a square with sidelength 8 inches

(b) The volume of a pyramid whose base is an equilateral triangle with sidelength one foot

Possible Answers:

(a) and (b) are equal.

(b) is greater.

(a) is greater.

It is impossible to tell from the information given.

Correct answer:

It is impossible to tell from the information given.

Explanation:

The volume of a pyramid is one-third of the product of the height and the area of the base. The areas of the bases can be calculated, but no information is given about the heights of the pyramids. There is not enough information to determine which one has the greater volume.

### Example Question #1 : How To Find The Volume Of A Pyramid

A pyramid with a square base has height equal to the perimeter of its base. Its volume is . In terms of , what is the length of each side of its base?

Possible Answers:

Correct answer:

Explanation:

The volume of a pyramid is given by the formula

where  is the area of its base and  is its height.

Let  be the length of one side of the square base. Then the height is equal to the perimeter of that square, so

and the area of the base is

So the volume formula becomes

Solve for :