p can do a work in 15 days and q cando the same work in 20 days . if they can work together for 4 days , what is the fraction of work left ?
amount of work p can do in 1 day = 1 / 15 amount of work q can do in 1 day = 1 / 20 amount of work p and q can do in 1 day = 1 / 15 + 1 / 20 = 7 / 60 amount of work p and q can together do in 4 days = 4 × ( 7 / 60 ) = 7 / 15 fraction of work left = 1 – 7 / 15 = 8 / 15 c
divide(subtract(const_60, multiply(divide(const_60, 15), add(divide(const_60, 15), divide(const_60, 20)))), const_60)