Subject: General Aptitude · Chapter: Time and Work · Exam: 2008 · Marks: · Difficulty:
25 men with 10 boys can do in 6 days as much work as 21 men with 30 boys can do in 5 days. How many boys must help 40 men to do the same work in 4 days?
(a)5
(b)10
(c)20
(d)40
Answer
Answer (as printed): B
Explanation
Let 1 man's 1 day's work = x and 1 boy's 1 day's work = y. Then, $6(25x + 10y) = 5(21x + 30y) \Rightarrow 150x + 60y = 105x + 150y \Rightarrow 45x = 90y \Rightarrow x = 2y$. Let the required number of boys be z. Then, $4(40x + zy) = 6(25x + 10y) \Rightarrow 4(80y + zy) = 6(50y + 10y)$ [since $x = 2y$] $\Rightarrow 80 + z = \frac{6 \times 60}{4} = 90 \Rightarrow z = 10$.
Explanation as extracted from the printed page; notation may be imperfect.