a man can do a job in 15 days . his father takes 10 days and his son finishes it in 25 days . how long will they take to complete the job if they all work together ?
"1 day work of the three persons = ( 1 / 15 + 1 / 10 + 1 / 25 ) = 21 / 150 so , all three together will complete the work in 150 / 21 = 7.1 days . answer : c"
divide(const_1, add(divide(const_1, 25), add(divide(const_1, 15), divide(const_1, 10))))