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A $16$ m deep well with diameter $3.5$ m is dug up and the earth from it is spread evenly to form a platform $27.5$ m $\times 7$ m. Find the height of the platform.
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(a) Volume of the earth dug up = $\frac{22}{7} \times \frac{7}{4} \times \frac{7}{4} \times 16 = 154$ m$^3$. Area of platform = $27.5 \times 7 = 192.5$ m$^2$. Height of platform = $\frac{154}{192.5} = \frac{4}{5}$ m or $80$ cm