Question

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.

Answer 1

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×(1000m)^2×10/100m`

`=7280×10^5m^3`

`=7.28×10^8m3`

Length of each river, l = 1072 km = 1072 × 1000 m = 1072000 m

Breadth of each river, b = 75 m

Depth of each river, h = 3 m

Volume of each river = l × b × h

= 1072000 × 75 × 3 m³

= 2.412 × 10⁸ m³

Volume of three such rivers = 3 × Volume of each river

= 3 × 2.412 × 10⁸ m³ 

= 7.236 × 10⁸ m³

Thus, the total rainfall is approximately same as the volume of the three river