Some persons can do a piece of work in 12 days. Two times the number of such persons will do half of that work in :
(a)6 days
(b)4 days
(c)3 days
(d)12 days
Answer
Answer (as printed): C
Explanation
Let $x$ men can do the work in 12 days and the required number of days be $z$. More men, Less days (Indirect Proportion). Less work, Less days (Direct Proportion). Men $2x:x$, Work $1:\frac{1}{2}$ :: $12:z$. $\therefore (2x \times 1 \times z) = \left(x \times \frac{1}{2} \times 12\right) \Leftrightarrow 2xz = 6x \Leftrightarrow z = 3$.
Explanation as extracted from the printed page; notation may be imperfect.