Discussion

If the volume of a cylinder is 900 cm³ and its height is 20 cm, then the diameter of the cylinder is

Answer: B

Rearrange the volume formula for the radius, then double it.

\[ V = \pi r^{2} h \quad\Longrightarrow\quad r^{2} = \frac{V}{\pi h} \]

\[ r^{2} = \frac{900}{3.142 \times 20} = \frac{900}{62.84} = 14.32 \]

\[ r = \sqrt{14.32} = 3.785 \text{ cm} \]

\[ d = 2r = 7.57 \text{ cm} \]

The question asks for the diameter, so the square root must be doubled - stopping at the radius leaves 3.79 cm.

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