Find the difference between the perimeter of a square with side length eleven centimetres and the perimeter of a square with side length ten centimetres. So remember a square is a quadrilateral in which all four sides are the same length and all four angles are ninety degrees. So I’ve sketched out an eleven-centimetre square and a ten- centimetre square here.
Now to work out the perimeter, that’s the distance all the way round the outside of the object. So for this square over here for example, the perimeter of the eleven-centimetre square is the length of this side plus the length of this side plus the length of this side plus the length of this side. And because each side is eleven centimetres long, to calculate that length of that perimeter is just four times eleven, which is forty-four. And the units are centimetres.
And the perimeter of the other square, again we’ve got the length of this side plus the length of this side plus the length of this side plus the length of this side. All four sides are ten centimetres, so that’s four times ten, which is forty centimetres.
Now the question asked us to find the difference between those two perimeters, and the difference between forty-four and forty can be calculated by doing a subtraction: forty-four take away forty, which is four centimetres. And don’t forget to include those units!
Now just before we go let’s have a look at another way of tackling that question. The lengths of the sides of those two squares were ten centimetres and eleven centimetres. So one square has a side length one centimetre bigger than the other, so the perimeter is gonna be four times this in difference. And four times one is four centimetres. We get the same answer, just a different method.