A and B can do a work in 5 days and 10 days respectively. A starts the work and B joins him after 2 days. In how many days can they complete the remaining work?  Choose one.
A) 5 days
B) 4 days
C) 3 days
D) 6 days
E) 9 days
Explanation:   1/7 + 1/14 + 1/28 = 7/28 = 1/4 =&gt; 4 days   answer 4 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 2 days. In how many days can they complete the remaining work?