If 6 men take 9 days to complete a work, how many men can complete the work in 3 days?

18 men

12 men

9 men

None of these

If 6 men take 9 days, total work = 6 × 9 = 54 man-days.

To finish in 3 days, number of men needed = 54 ÷ 3 = 18 men.