Calculating Grids - Maths

In Maths we have been learning how to calculate the perimeter of a square without the 4 corners. There are 6 theories and ways to work this out but I'm doing the easiest ways . There are 2 easy theories which are 4 +10 + 10 + 10 +10 - or 8 + 8 + 8 + 8 + 8 - 4. Below I will have the way to do it for the 2 easiest ways in my opinion.

This form is one of the easiest forms here. All you have to do it add up how many squares are in perimeter of the box then take away the amount of red squares to get the answer it should look like this. 10 + 10 + 10 + 10 - 4 = 36 or you can do the algebraic way which is n + n + n + n - 4 = 36 or a simpler way that is 
4n - 4 = 36.

This form is the second easiest one for me.In this form all we have to do is calculate both red and blue sides. The red side = 10 and the blue side = 8. The way you work this out is by doing 10 + 8 + 10 + 8 = 36 or the algebraic way which is n + 8 + n + 8 = 36





Here are some of the grids if you want to try and work them out for yourself. If you know any easier ways to calculate the 2 that I showed comment them down!