Find a Missing Prism Height

Supplied materials

• Paper and a pencil; drawing and spoken explanations are welcome. An adult may read directions and options aloud.
• Supplied worked-case record: A prism has volume 120 cubic cm and base 5 cm by 4 cm.
• All quantities and shape descriptions are supplied in the worked example and questions; no purchase or personal information is needed.

Learn the idea

Prism volume equals base area times height. Dividing volume by the known base area recovers height. The base area uses square units and volume uses cubic units, so their quotient is an ordinary length. A missing dimension is not found by subtracting the two known side lengths from volume.

Calculate base area from the two supplied side lengths. Divide the supplied volume by that area to find height. Multiply all three dimensions to verify the recovered height and label the answer in length units.

Find the base area before dividing volume. Report the recovered height in length units. Write V = base area × height with a blank for the missing dimension.

1. Write V = base area × height with a blank for the missing dimension.
2. Follow the worked example. Point to each number or shape feature and say what it tells you.
3. Calculate base area from the two supplied side lengths.
4. Try the question and then the three practice questions. Check your answers and explain any change you make.

Check your reasoning

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Take it further

Volume 210 cubic cm, base 7 by 5 cm: expected height 6 cm.

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