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# Surface Areas And Volumes

#### Question 4:

In one fortnight of a given month, there was a rainfall of 10 cm in a river valley. If the area of the valley is 7280 km2, show that the total rainfall was approximately equivalent to the addition to the normal water of three rivers each 1072 km long, 75 m wide and 3 m deep.

Area of the valley = 7280 km2

If there was a rainfall of 10 cm in the valley then amount of rainfall in the valley = Area of the valley × 10 cm

Amount of rainfall in the valley = 7280 km2 × 10 cm
$=7280×{\left(1000\mathrm{m}\right)}^{2}×\frac{10}{100}\mathrm{m}\phantom{\rule{0ex}{0ex}}=7280×{10}^{5}{\mathrm{m}}^{3}\phantom{\rule{0ex}{0ex}}=7.28×{10}^{8}{\mathrm{m}}^{3}$

Length of each river, l = 1072 km = 10…

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