Maths NCERT. Ex. 13.5 - Q . No. 4
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Q 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 97280 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.Solution: Area of the valley, A = 97280 km2Level in the rise of water in the valley, h = 10 cm = (10/100000) km = (1/10000) kmThus, amount of rain fall in 14 day = Ah = 97280 km2 × (1/10000) km = 9.828 km3Amount of rain fall in 1 day = 9.828 /14 = 0.702km3Volume of water in 3 rivers = length × breadth × height = 1072 km × 75 m × 3 m = 1072 km × (75/1000) km × (3/1000) km = 0.2412 km3 x3 = 0.7236 km3This shows that the amount of rain fall is approximately equal to the amount of water in three rivers.
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