Part of tank filled by tap A in 1 hour = 1/10 Part of tank filled by tap B in 1 hour = 1/12 Part of tank filled by tap C in 1 hour = 1/15 ⇒ Part of tank filled by all three taps in 1 hour = 1/10 + 1/12 + 1/15 = 15/60 = 1/4 ∴ The complete tank will be filled in 4 hours.