A man can do a piece of work in 5 days. With help of his son, he can do it in 3 days. In what time can the son do it alone?

🧠 Explanation:

A man works in 5 days, with his son in 3 days, so the son alone takes 7.5 days. Solve: man’s rate = 1/5, together 1/3, son’s rate = 1/3 - 1/5 = 2/15, so time = 15/2 = 7.5. This teaches work rate math.