A , B and C can complete a work in 2 h. If A does the job alone in 6 h and B in 5 h, how long will it take for C to finish the job alone?

Let C alone can finish the job in T hours.
According to the question,
Work done by A, B and C in 1h = 1/2
⇒ 1/6 +1/5 + 1/T = 1/2
⇒ 1/T = 1/2 - 1/6- 1/5 = (15 - 5- 6)/30
⇒ 1/T = 4/30 = 2/15
∴ T = 7¹/₂ h