1.  A and B can complete a work in 15 days and 10 days respectively. They started doing the work together but after 2 days B had to leave and A alone completed the remaining work. The whole work was completed in :

A. 8 days
B. 10 days
C. 12 days
D. 15 days

Answer: Option C

Explanation:

(A + B)'s 1 day's work = ( 1 + 1 ) = 1 .
15 10 6

Work done by A and B in 2 days = ( 1 x 2 ) = 1 .
6 3

Remaining work = ( 1 - 1 ) = 2 .
3 3

Now, 1 work is done by A in 1 day.
15

Therefore 2 work will be done by a in ( 15 x 2 )
3 3

= 10 days.

Hence, the total time taken = (10 + 2) = 12 days.