A man is twice as fast as a woman and a woman is twice as fast as a boy in doing a work. If all of them a man, a woman and a boy can finish a piece of work in 7 days, then in how many days a boy will do it alone?

49 45 40 42

49

ATQ, Efficiency ratio: Man : Women : Boy = 4 : 2 : 1 = 7R (total) Total Work = Efficiency × time = 7 × 7 = 49 The boy alone will do it in = \(\frac{49}{1}\) = 49 days