a can do a job in 15 days and b can do it in 30 days . a and b working together will finish twice the amount of work in days ?
"1 / 15 + 1 / 30 = 3 / 30 = 1 / 10 10 = 10 * 2 = 20 days answer : a"
add(divide(const_1, 15), divide(const_1, 30))