A lampshade is a frustum with bottom radius 120 mm, top radius 70 mm, and vertical height 200 mm. Fi

Question

A lampshade is a frustum with bottom radius 120 mm, top radius 70 mm, and vertical height 200 mm. Find the slant height $h$ of the frustum.[2] The net is an annular sector. Its inner radius is $r_1$ mm and its outer radius is $r_1+h$ mm. Show that $r_1=288.6$ mm.[3] Hence, find $\theta$.[1] Calculate the amount of material needed for the lampshade, in square centimetres.[2]

Accepted Answer

(a) $206\text{ mm}$ (b) $288.6\text{ mm}$ (c) $87.3^\circ$ (d) $1230\text{ cm}^2$

2025 SST PRELIMS P1 Q22

2025 SST PRELIMS P1 Q22

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