# 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 km^{2}, 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.

#### Answer:

Area of the valley = 7280 km^{2}

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 km^{2} × 10 cm

$=7280\times {\left(1000\mathrm{m}\right)}^{2}\times \frac{10}{100}\mathrm{m}\phantom{\rule{0ex}{0ex}}=7280\times {10}^{5}{\mathrm{m}}^{3}\phantom{\rule{0ex}{0ex}}=7.28\times {10}^{8}{\mathrm{m}}^{3}$

Length of each river, *l* = 1072 km = ...

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