A and B can do a piece of work alone in 15 and 30 days respectively. In how many days can they together complete the work?

10 8 9 12

10

A = 15 days, B = 30 days, ⇒ A + B can complete the work in = \(\frac{30}{2+1}\) = \(\frac{30}{3}\) = 10 days,  ..(\(\frac{Work}{Efficiency}\) = Time)