2 men and 4 boys can do a piece of work in 10 days, while 4 men and 5 boys can do it in 6 days. Men and boys are paid wages according to their output. If the daily wage of a man is Rs 40, then the ratio of daily wages of a man and a boy will be -

Let m be man's work per day, b be boy's work per day. From given: 2m + 4b = 1/10 and 4m + 5b = 1/6. Solving gives m = 1/70, b = 1/140. So a man does twice the work of a boy. If man's wage is Rs 40, boy's wage should be Rs 20 (since wages are proportional to output). Ratio = 40:20 = 5:2. Common mistake is not solving the equations correctly.