If it takes 10 men to build a house in 6 months how many men would be needed to build it in 4 months

Answer 1

10 men to build a 1 house in 6 months
10 men to build a 1/6 house in 1 months
10 men to build a 4/6 house in 4 months
1 man to build a 4/60 house in 4 months
60/4 men can build 1 house in 4 months

15 men can build 1 house in 4 months

or more simply
it takes 60 man-months to build the house
so it takes (60 man-months/4 months) men or 15 men to build the house
(the units of months would cancel)

Answer 2

60