a can do a piece of work in 10 days and b alone can do it in 15 days . how much time will both take to finish the work ?
"c 6 days time taken to finish the job = xy / ( x + y ) = 10 x 15 / ( 10 + 15 ) = 150 / 25 = 6 days"
divide(const_1, add(divide(const_1, 10), divide(const_1, 15)))