A and B two taps fill in a tank in 5 hours and 10 hours respectively. If both tapes are opened together, the tank will be full in:

Question: A and B two taps fill in a tank in 5 hours and 10 hours respectively. If both tapes are opened together, the tank will be full in:

Solution:
A's 1 hour's work = 1/5
B's 1 hour's work = 1/10

(A+B)'s 1 hour's work = (1/5) + (1/10)
= (2 + 1)/10
= 3/10

Now,
3/10 parts both the taps can fill the tank in 1 hour
∴ 1 part both the taps can fill the tank in 10 × (1/3) hours
= 10/3 hours

∴ The tank will be full in 10/3 hours.