a can do a work in 15 days and b in 20 days . if they work on it together for 6 days , then the fraction of the work that is left is
"person ( a ) ( b ) ( a + b ) time - ( 15 ) ( 20 ) ( - ) rate - ( 20 ) ( 15 ) ( 35 ) work - ( 300 ) ( 300 ) ( 300 ) therefore a + b requires ( 300 / 35 ) days to complete entire work for 1 st 4 days they work 35 * 6 = 210 remaining work is 300 - 210 = 90 remaining fraction of work is = 90 / 300 = 3 / 10 answer c"
subtract(const_1, multiply(add(divide(const_1, 15), divide(const_1, 20)), 6))