A and B can do a work in 5 days and 10 days respectively. A starts the work and B joins him after 4 days. In how many days can they complete the remaining work?
Choices:
A) 6 days  B) 2/3 days  C) 8 days  D) 3 days  E) 9 days
Work done by A in 4 days = 4/5   Remaining work = 1/5   Work done by both A and B in one day = 1/5 + 1/10 = 3/10   Remaining work = 1/5 * 10/3 = 2/3 days.   Answer: 2/3 days
<result>B</result>
A and B can do a work in 5 days and 10 days respectively. A starts the work and B joins him after 4 days. In how many days can they complete the remaining work?