a can do a job in 15 days and b in 20 days . if they work on it together for 5 days , then the fraction of the work that is left is ?
"a ' s 1 day work = 1 / 15 b ' s 1 day work = 1 / 20 a + b 1 day work = 1 / 15 + 1 / 20 = 7 / 60 a + b 5 days work = 7 / 60 * 5 = 7 / 12 remaining work = 1 - 7 / 12 = 5 / 12 answer is d"
subtract(const_1, multiply(5, add(divide(const_1, 15), divide(const_1, 20))))