What's the fastest way to do these math problems?

jamesford
Sun, 30 Aug 2009 19:08:30 +0000

On a square gameboard that is divided into n rows of n squares each, k of these squares lie along the boundary of the gameboard. Which of the following is a possible value for k?

A 10
B 25
C 34
D 42
E 52

The number of squares along the border is n + (n-2) + (n-2) + n = k. Then
4n - 4 = k
n -1 = k/4
n = k/4 + 1

Since we can’t have fractions of a square, k must be divisible by 4. The only choice divisible by 4 is E, 52.