Five men and nine women can do a piece of work in 10 days. Six men and twelve women can do the same work in 8 days. In how many days can three men and three women do the work ?

Correct Answer: 20 days

(5m + 9w)10 = (6m + 12w)8 

=> 50m + 90w = 48w + 96 w    => 1m = 3w

5m + 9w = 5m + 3m = 8m

 

8 men can do the work in 10 days.

3m +3w = 3m + 1w = 4m

So, 4 men can do the work in (10 x 8)/4 = 20 days.