A wall of 100 metres can be built by 7 men or 10 women in 10 days. How many days will 14 men and 20 women take to build a wall of 600 metres?
(a)15
(b)20
(c)25
(d)30
Answer
Answer (as printed): A
Explanation
Let the required number of days be $x$. 7 men $\equiv$ 10 women $\Rightarrow$ 14 men $\equiv$ 20 women. $\therefore$ (14 men and 20 women) $\equiv (20+20)$ women $= 40$ women. More length, More days (Direct Proportion). More women, Less days (Indirect Proportion). Length $100:600$, Women $40:10$ :: $10:x$. $\therefore 100 \times 40 \times x = 600 \times 10 \times 10 \Leftrightarrow x = \frac{600 \times 10 \times 10}{100 \times 40} = 15$.
Explanation as extracted from the printed page; notation may be imperfect.