5 men and 12 boys finish a piece of work in 4 days, 7 men and 6 boys do it in 5 days. The ratio between the efficiencies of a man and boy is? Pick:
A) 6 : 8
B) 6 : 4
C) 6 : 2
D) 6 : 5
E) 6 : 2

Rationale: 5 m + 12 b - - - - - 4 days 7 m + 6 b - - - - - - - 5 days 20 m + 48 b = 35 m + 30 b 18 b = 15 m = > 5 m = 6 b m : b = 6 : 5 answer : d
Answer: D