6 men can complete the electric fitting in a building in 7 days. How many days will it take if 21 men do the job?

Explanation

`6` men can complete the work in `=7` days
`1` man will complete the same work in
`= 7*6` days
(Less men, more days)
` therefore 21` men will finish the work in
`=
7*6/21` days
(More men, less days)
`=2` days.