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? Choices.
A) 6:6 B) 6:1 C) 6:9 D) 6:5 E) 6:2
5M + 12B ----- 4 days   7M + 6B ------- 5 days   20M + 48B = 35M + 30B   18B = 15M =&gt; 5M = 6B   M: B = 6:5   Answer: 6:5
<result>D</result>
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?