X can do a piece of work in 40days. He works at it for 8days and then Y finished it in 16days. How long will Y take to complete the work?  Choose the correct choice from the following choices.
A) 10
B) 12
C) 15
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 16 days whole work will be done by y in 16 * 5 / 4 = 20 days answer is e"
Answer: E