Question

A box contains a collection of triangular and square tiles. There are 25 tiles in the box, containing 84 edges total. How many square tiles are there in the box?

Answer 1

triangular and square tiles all the 3 sides - the difference is that square tiles have one side more!

when we first think about the 3 sides: the 25 tiles must then have at least 25*3=75 sides.

But they have 84. what is the difference? there are 84-75=9 extra sides, which means that there are 9 square tiles.