A single reservoir supplies the petrol to the whole city, while the reservoir is fed by a single pipeline filling the reservoir with the stream of uniform volume. When the reservoir is full and if 40, 000 litres of petrol is used daily, the supply fails in 90 days. If 32, 000 litres of petrol used daily, it fails in 60 days. How much petrol can be used daily without the supply ever failing?

Explanation:-

Let X litres be the per day filling and L litres be the capacity of the reservoir, then
90X + L = 40000 × 90 ----------- (1)
60X + L = 32000 × 60 ----------- (2)
Solving the equation,
X = 56000 litres
Thus, 56000 litres per day can be used without the failure of supply.