GED Math Extra Prep: Volume and Surface Area of Prisms

By Consumer Dummies

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

  1. 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

  2. If these two boxes have the same volume, what is the height of the second box?

    ged-volume

    A. 4
    B. 5
    C. 8
    D. 10

Answers and Explanations

  1. 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 = 6s2

    You know the surface area equals 216 cubic inches, so you can substitute this into the equation for SA and solve for s:

    216 = 6s2

    Dividing both sides by 6 gives you

    36 = s2

    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.

  2. 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:

    GED_1801

    Therefore, Choice (B) is the correct answer.