Question

A worker can build a fence in 8 hours, With the help of an assistant, the fence can be built in 5 hours. How long should it take the assistant, working alone, to build the fence?

Answer 1

I am not certain but I think this is right. With both worker and assistant the fence is built in 62.5% the time that it takes just the worker. So the assistant is 12.5% slower than the worker and it takes him 9 hours to build the fence alone.