If 12 men and 6 boys can do a work in 4 days and 4 men and 14 boys can do the same work in 8 days, find the ratio of efficiency of a man to that of a boy. 

12 men and 6 boys can complete the work in 4 days.

4 men and 14 boys can complete the work in 8 days. 

Formula Used: 

Total Work = Number of Workers × Efficiency × Time. 

Let man be denoted as m and boys be denoted as b
(12m + 6b) × 4 = (4m + 14b) × 8.
 (12m + 6b) = (4m + 14b) × 2
12m + 6b= 8m + 28b.
4m = 22b
​$$\frac{m}{b} =\frac{11}{2}$$​​
So required ratio is 11 : 2 ​