A and B can do a job in 15 days and 10 days, respectively. They began the work together but A leaves after some days and B finished the remaining job in 5 days. After how many days did A leave? Choose one.
A) 2 days	B) 3 days	C) 1 day	D) 4 days	E) None of these
A’s one day’s work = 1⁄15 th work.   B’s one day’s work = 1⁄10 th work.   (A + B)’s one day’s work = 1⁄15 + 1⁄10 = 1⁄6 th work.   Let A left after x days.   ∴ (A + B)’s x days’ work = x⁄6 th work.   Remaining work = 1 - x⁄6 = (6 - x)⁄6 th work.   Now, in 5 days, work done by B = (6 - x)⁄6 th work.   ∴ in 1 day work done by B = (6 - x)⁄30 th work.   and (6 - x)⁄30 = 1⁄10   ∴ x = 3 days   Answer 3 days
<result>B</result>
A and B can do a job in 15 days and 10 days, respectively. They began the work together but A leaves after some days and B finished the remaining job in 5 days. After how many days did A leave?