Given: A and B can do a piece of work in 10 days and 15 days respectively Concept Used: One day work = 1/number of days taken by the worker to complete the whole work Calculation: One day work of A =1/10 One day work of B =1/15 One day work of A+B=1/10+1/15 ⇒(3+2)/30 ⇒1/6 Now, 3 days work done by (A + B) is 3×1/6 ⇒1/2 Hence, the part of work they can do together in 3 days is 1/2 of the whole work