Solution

153222

Problem / game
An appearing act Back to problem
First name
Ciaran Carroll
School
Pnins
Country
New Zealand
Age
12

It's because the two right angled triangles may look like the hypotenuse of the two may look like they're on the same angle, but they're actually sloped at slightly different angles. This causes a 1x1 square to appear in the 13x5 square.