A can do a job in 10days and B in 20days. If they work on it together for 4 days, then the fraction of the work that is left is?  Choices.
A) 2/5 B) 8/15 C) 3/11 D) 1/12 E) 6/13
2/5's 1 day work = 1/10   B's 1day work = 1/20   2/5+B 1day work = 1/10 + 1/20 = 3/20   2/5+B 4days work = 3/20*4 = 3/5   Remaining work = 1 - 3/5 = 2/5   2/5nswer is 2/5
<result>A</result>
A can do a job in 10days and B in 20days. If they work on it together for 4 days, then the fraction of the work that is left is?