A does a work in 10 days and B does the same work in 30 days. In how many days they together will do the same work ? Select.
A) 5.5 days  B) 6.5 days  C) 7.5 days  D) 8.5 days  E) None of these
Explanation:   Firstly we will find 1 day work of both A and B, then by adding we can get collective days for them,   So,   A's 1 day work = 1/10   B's 1 day work = 1/30   (A+B)'s 1 day work =   (1/10+1/30)=2/15   So together they can complete work in 7.5 days.   Answer: 7.5 days
<result>C</result>
A does a work in 10 days and B does the same work in 30 days. In how many days they together will do the same work ?