Working 8 hours a day, 12 men can do a work in 30 days. Working 4 hours a day, 18 men can do the work in (P.C.S., 2006)
(a)30 days
(b)40 days
(c)45 days
(d)50 days
Answer
Answer (as printed): B
Explanation
Let the required number of days be $x$. Less working hours, More days (Indirect Proportion). More men, Less days (Indirect Proportion). Working hours $4:8$, Men $18:12$ :: $30:x$. $\therefore 4 \times 18 \times x = 8 \times 12 \times 30 \Leftrightarrow x = \left(\frac{8 \times 12 \times 30}{4 \times 18}\right) = 40$.
Explanation as extracted from the printed page; notation may be imperfect.