Squares everywhere

Probability Level 2

In the following $3 \times 4$ square grid, how many squares are there, whose perimeter is formed by the grid lines?

1 solution

Arron Kau Staff
May 13, 2014

Let's count the 1 by 1 squares. There are $3 \times 4 = 12$ of them.

Let's count the 2 by 2 squares. There are $2 \times 3 = 6$ of them.

Let's count the 3 by 3 squares. There are $1 \times 2 = 2$ of them.

Hence, by the rule of Sum there are $12 + 6 + 2 = 20$ squares in total.