A can finish a piece of work in 6 days and B can finish it in 12 days. How many days will they take working together?

💡 Solution & Explanation

In one day A does 1/6 of the work and B does 1/12. Together they do 1/6 + 1/12 = 1/4 of the work per day. So the whole work takes 4 days. Shortcut: ab ÷ (a + b) = 72 ÷ 18 = 4. Together they must be faster than either one alone.