a can do a job in 10 days and b in 20 days . if they work on it together for 4 days , then the fraction of the work that is left is ?
"a ' s 1 day work = 1 / 10 b ' s 1 day work = 1 / 20 a + b 1 day work = 1 / 10 + 1 / 20 = 3 / 20 a + b 4 days work = 3 / 20 * 4 = 3 / 5 remaining work = 1 - 3 / 5 = 2 / 5 answer is a"
subtract(const_1, multiply(4, add(divide(const_1, 10), divide(const_1, 20))))