A and B can complete a work in 20 days and 30 days respectively. A works full time but B works half time. In how many days the entire work is to be completed?

15 days

A = 20 days, B = 30 days,

⇒ As B works half time, therefore his efficiency will be taken as half of original i.e; Half of 2 = 1,

⇒ Time required by A + B to complete the work = \(\frac{60}{3+1}\) = \(\frac{60}{4}\) = 15 days.     ..(\(\frac{Work}{Efficiency}\) = Time)