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 97280 km sq., show that the total rainfall was approximately equal to the addition to the normal wate of 3 rivers each 1072 km long, 75m wide & 3m wide.

Answer 1

Area of the valley =97280 km²
Height of rainfall in valley = 10cm = 10 × 10⁻⁶ = 10⁻⁵ km
Now, volume of rain water in valley = area of the valley × height of rainfall into valley = 97280 × 10⁻⁵ km³ = 0.9728 km³
Volume of water in valley 0.9728 km³ in 14days [ according to question ]
So, volume of water in valley in 1 day = 0.9728/14 ≈ 0.7 km³

Now, volume of each river = length × Breadth × height
= 1072km × 75m × 3m
= 1072 × 75 × 10⁻³ × 3 × 10⁻³ km³
= 0.2412 km³

So, volume of 3 rivers = 3 × volume of each river
= 3 × 0.2412 km³
= 0.7236 km³ ≈ 0.7 km³

Here it is clear that approximately volume of water in valley {means volume of rainfall water } = volume of water in 3 rivers