# GED Math Extra Prep: Volume and Surface Area of Prisms

The GED Math test will throw some geometry questions at you that involve three-dimensional shapes like prisms. Usually, they will be in the form of a cube or box, as in the following practice questions.

## Practice Questions

- A cube has a surface area of 216 square inches. What is its volume in cubic inches?
**A.**6

**B.**36

**C.**108

**D.**216 - If these two boxes have the same volume, what is the height of the second box?
**A.**4

**B.**5

**C.**8

**D.**10

## Answers and Explanations

- The correct answer is D.
You can determine the surface area

*(SA)*of a cube with the following equation, in which*s*is the length of a side:*SA*= 6*s*^{2}You know the surface area equals 216 cubic inches, so you can substitute this into the equation for

*SA*and solve for*s:*216 = 6

*s*^{2}Dividing both sides by 6 gives you

36 =

*s*^{2}Hence,

*s*= 6.A cube is a special type of rectangular prism in which the length

*(l),*the width*(w),*and the height*(h)*are all equal. The volume of a rectangular prism is given by*V*=*lwh*Substituting

*l*= 6,*w*= 6, and*h*= 6 into the equation shows the volume equals 216 cubic inches. Hence, Choice (D) is the correct answer. - The correct answer is B.
The volume of a box (rectangular prism) is

*V*=*lwh*, where*l*is the length,*w*is the width, and*h*is the height. Set the volumes of the two boxes equal to each other and solve for*h:*Therefore, Choice (B) is the correct answer.