Question: If it takes 8 days for 3 builders to build a cottage. How long will it take 6 builders to build the same size cottage working at the same rate?
Give me a detailed solution. 
Answer: 
It would take one builder 8 x 3 = 24 days to build the cottage on his own.
6 builders can build the house in 24 / 6 = 4 days.