A can do a work 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 :  Pick one.
A) 1/3	B) 7/12	C) 5/12	D) 2/3	E) 1/2
Ans is:C   A's 1 day's work =1/15   B's 1 day's work =1/20   (A + B)'s 1 day's work =(1/15+1/20)=7/60   (A + B)'s 5 day's work =(7/60*5)=7/12   Therefore, Remaining work =(1-7/12)=5/12. Answer: 5/12
<result>C</result>
A can do a work 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 :