A and B can complete a work in 30days and 15day. They started doing the work together but after 5days B had to leave and A alone completed the remaining work. The whole work was completed in?  Options
A) 10 days  B) 12 days  C) 20 days  D) 18 days  E) 25 days

Rationale: a + b 1 day work = 1 / 30 + 1 / 15 = 1 / 10 work done by a and b in 10 days = 1 / 10 * 5 = 1 / 2 remaining work = 1 - 1 / 2 = 1 / 2 now 1 / 30 work is done by a in 1 day 1 / 2 work will be done by a in 30 * 1 / 2 = 15 days total time taken = 15 + 5 = 20 days answer is c
Answer: C