71.

Water is pouring into a cuboidal reservoir at the rate of 60 litres per minute. If the volume of reservoir is 108 m³, find the number of hours it will take to fill the reservoir.

Volume of the reservoir = 108 m³
∵                           1 m³ = 1000 litres
∴      Capacity of the reservoir = 108 x 1000 litres
                                                = 108000 litres
            Amount of water poured in 1 minute = 60 litres
∴      Amount of water to be poured in 1 minute = 60 x 60 litres
   Thus, number of hours required to fill the reservoir = 
∴  The required number of hours = 30