WAEC 2020 · Paper 1 · Q28

Solid mensuration

The dimensions of a rectangular base of a right pyramid are $9\text{ cm}$ by $5\text{ cm}$ . If the volume of the pyramid is $105\text{ cm}^3$ , how high is the pyramid?

Worked solution (try it first)

Volume of a pyramid: $\frac13 \times \text{base area} \times h$ .
The base area is $9 \times 5 = 45\text{ cm}^2$ .
$\frac13 \times 45 \times h = 105$ , so $15h = 105$ .
So $h = 7$ cm, option D.

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