12 persons can do a piece of work in 4 days. How many persons are required to complete 8 times the work in half the time?
(a)144
(b)180
(c)190
(d)192
Answer
Answer (as printed): D
Explanation
Let the required number of persons be $x$. Less days, More persons (Indirect Proportion). More work, More persons (Direct Proportion). Days $2:4$, Work $1:8$ :: $12:x$. $\therefore 2 \times 1 \times x = 4 \times 8 \times 12 \Leftrightarrow x = \frac{4 \times 8 \times 12}{2} = 192$.
Explanation as extracted from the printed page; notation may be imperfect.