Bihar Police Constable Model Paper 2

Given:
Three pipes A, B, and C can fill a tank in 20, 15, and 30 hrs respectively. All the pipes are open at the same time.
Concept used:
Pipe and cistern
Calculation:
Three pipes A, B and C fill a tank in 20,15 and 30 hrs.
To find the total work we take the lcm of 20,15 and 30.
Total work is 60 units.
Individual work of A = 60/20 = 3 units
Work of B = 60/15 = 4 units
Work of C = 60/30 = 2 units
All the pipes are open at the same time
⇒ $\frac{60}{3+4+2}$
⇒ $\frac{60}{9}$
∴ 6.67 hours