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.

Rainfall in the velley = 10 cm = 0.1 m. Area of valley = 97280 km² = 97280000000 m²
Volume of rain water = 97280000000 × 0.1 = 9728000000 m³
Volume of one river = 1072000 × 75 × 3 = 241200000 m³
Volume of there rivers = 3 × 241200000 = 723600000 m³
Hence, 723600000 m³ ≈ 9728000000 m³