a can do a work in 15 days and b in 20 days . if they work on it together then in how many days required to complete the work ?
person ( a ) ( b ) ( a + b ) time - ( 15 ) ( 20 ) ( 300 / 35 ) rate - ( 20 ) ( 15 ) ( 35 ) work - ( 300 ) ( 300 ) ( 300 ) therefore a + b requires ( 300 / 35 ) days to complete entire work = 300 / 35 answer is b
inverse(add(divide(const_1, 15), divide(const_1, 20)))