X can do a piece of work in 40days. He works at it for 8days and then Y finished it in 20 days. How long will Y take to complete the work? Choose the most appropriate option.
A) 10  B) 12  C) 25  D) 18  E) 20

Rationale: "work done by x in 8 days = 8 * 1 / 40 = 1 / 5 remaining work = 1 - 1 / 5 = 4 / 5 4 / 5 work is done by y in 20 days whole work will be done by y in 20 * 5 / 4 = 25 days answer is c"
Answer: C