A straight fence is to be constructed from posts 6 inches wide and separated by lengths of chain 5 feet long. If a certain fence begins and ends with a post, which of the following could not be the length of the fence in feet? (12 inches = 1 foot)
A. 17
B. 28
C. 35
D. 39
E. 50
Well, to get the possible length you start with 6 in (0.5 feet) and add 5.5 feet multiple times. You could get 6, 11.5, 17, 22.5, 28, 33.5, 39, 44.5, 50, ... Notice we missed the "35" option, which is, thus, not possible.
