A can do a work in 20 days and B in 30 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 answers:	A) 1/3	B) 2/3	C) 4/3	D) 5/3	E) 7/3
Ans is:2/3   A's 1 day's work =1/20   2/3's 1 day's work =1/30   (A + 2/3)'s 1 day's work =(1/20+1/30)=1/12   (A + 2/3)'s 4 day's work =(1/12*4)=1/3   Therefore, Remaining work =(1-1/3)=2/3
<result>B</result>
A can do a work in 20 days and B in 30 days. If they work on it together for 4 days, then the fraction of the work that is left is :