a man can do a piece of work in 10 days , but with the help of his son , he can finish it in 5 days . in what time can the son do it alone ?
"son ' s 1 day work = 1 / 5 - 1 / 10 = 1 / 10 son alone can do the work in 10 days answer is d"
divide(multiply(10, 5), subtract(10, 5))