DRDO Multi tasking staff Model paper 3

Let tank capacity be x Liters
Initially tank was filled 1/4 ‌th of x and after removing 4 liters it was filled to 1/5 ‌th of x.
∴

x

4

−

x

5

=4
⇒

5x−4x

20

=4
⇒ x = 20 × 4 = 80 Liters
∴ Capacity of tank is 80 Liters