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Question:

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

Solution:

Given: Area of the valley = 7280 km²
Volume of rainfall in the area = 7280 × 10 × 0.00001 = 0.728 km³ (Converting 1cm to km)
Volume of water in 3 rivers = 3 × l × b × h
(3 × Volume = 3 × l × b × h) = 3 × 1072 × 75 × 0.001 × 3 × 0.001 (Converted 1m to km) = 0.723 km³
So, the two volumes are nearly similar.