12 men and 18 boys working 7.5 minutes an hour complete a particular piece of work in 60 hours. If a boy’s work is half as efficient as a man’s work, how many boys will be needed to help 21 men to achieve twice the work in 50 hours working 9 minutes in an hour. Choose the correct choice from the following choices:
A) 28
B) 77
C) 42.
D) 99
E) 17
Explanation:   1 man is equivalent to 2 boys in work capacity. 12 men + 18 boys = 12 x 2 + 18 = 42 boys.   Let the required number of boys be x. So Total number of people doing work = 21 men x 2 (according to work capacity) + x boys.   Taking respective ratios as required:   Given:   =&gt; Hours 50:60   =&gt; Minutes per hour 9: 15/2   =&gt; Work 1:2   =&gt; People: 42: 42 + x   =&gt; 50 x 9 x 1 x (42+x) = 60 x 15/2 x 2 x 42   =&gt; 42 +x = 84   x = 42   ANSWER:42.
<result>C</result>
12 men and 18 boys working 7.5 minutes an hour complete a particular piece of work in 60 hours. If a boy’s work is half as efficient as a man’s work, how many boys will be needed to help 21 men to achieve twice the work in 50 hours working 9 minutes in an hour.