In a Lake, there is a patch of lily pads. Every day, the patch doubles in size. It takes 39 days for the patch to cover the entire lake, how many days would it take the patch to cover half of the lake?
Choose the most appropriate option.
A) 36 B) 2 ^ 4 * 3 C) 24 D) 38 E) 47

Rationale: "working backward from the day it ' s covered : day 39 : fully covered day 38 : half covered so 38 days answer : d"
Answer: D