A, B and C working together can do a piece of work in 8 hours. A alone can do it in 20 hours and B alone can do it in 24 hours. In how many hours will C alone do the same work?

The correct answer is: 30 hours.

Let’s say the total work is represented as w
Step 1 of 2:
It is given that A alone can do the full work in 20 hours and B alone can do the full work in 24 hours and Let’s say that C alone can do the full work in t hours
So, work done by A in 1 hour = 
Work done by B in 1 hour = 
Work done by C in 1 hour = 
Step 2 of 2:
It is also given that A, B and C working together can do a piece of work in 8 hours. So we can write
Work done by A in 8 hours + Work done by B in 8 hours + Work done by C in 8 hours = w
 8 +   8 +   8 = w
8w( +  + ) = w



t = 30 hours
Final Answer:
Hence, C alone can do the same work in 30 hours.