Blue book pg 681 # 7

UnleashedFury
Thu, 22 Nov 2007 14:43:11 +0000

^wouldn’t have thought of it like that in a million years.

i just thought:

1
4
9
16
25

25 - x = 7; x = 18, which doesn’t work
16 - x = 7; x = 9, which means your answer is 4

seems sort of elementary, but it works and it’s fast. well under 30 seconds.