Calculating the area and permiter of 2D shapes

In Year 10, we have been learning about calculating the area and perimeter of 2D shapes. Shapes that we have been looking at include rectangles, triangles, parallelograms and trapeziums.

Below is a problem that we looked at using perimeters of congruent rectangles. Have a go and see if you can answer the problem!

Area and perimeter

The word congruent means that two (or more) objects have the exact same size even if one is a rotation of the other. What this means is that all of the bricks in the question are all of the same length

The word perimeter describes the total distance around all of the shape.

Solution

When we look at the yellow highlighted sections, they all represent the same height of 13cm.

Since there are two of them on the bricks in the left-hand side, there total is 2 x 13 = 26cm. This means the remaining height (the red arrow) has got to be 33 – 26 = 7cm.

Since the red arrow is 7cm, the total of the two blue arrows must be 13 – 7 = 6cm. Since the two blue arrows are 6cm, each one must be 3cm.