A can do a work in 15 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 :	Choose the correct choice from the following options
A) 1/10
B) 8/15
C) 6/15
D) 1/15
E) none of the above
Ans is:8/15   A's 1 day's work =1/15   8/15's 1 day's work =1/20   (A + 8/15)'s 1 day's work =(1/15+1/20)=7/60   (A + 8/15)'s 4 day's work =(7/60*4)=7/15   Therefore, Remaining work =(1-7/15)=8/15
<result>B</result>
A can do a work in 15 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 :