A village, having a population of 4000, requires 150 litres of water per head per day. It has a tank measuring 20 m × 15 m × 6 m. For how many days will the water of this tank last?

Length of tank l = 20 m, Breadth b = 15 m and height h = 6 m
Volume of tank = lbh = 20 × 15 × 6 = 1800 m³ = 1800 × 1000 = 1800000 litres
Daily requirement of water = 150 litres
Therefore, the requirement of 4000 person for one day = 150 × 4000 = 600000 litres
Hence, the number of days to consume all water of tank
Volume of tank/Volume of water for 4000 person for one day
= 1800000 litres/600000 litres = 3