New
New
Year 4
Know that unknown side lengths can be calculated from the perimeter and known side lengths
I can calculate unknown side lengths of rectangles from the perimeter and known side lengths.
New
New
Year 4
Know that unknown side lengths can be calculated from the perimeter and known side lengths
I can calculate unknown side lengths of rectangles from the perimeter and known side lengths.
These resources will be removed by end of Summer Term 2025.
Switch to our new teaching resources now - designed by teachers and leading subject experts, and tested in classrooms.
Lesson details
Key learning points
- Subtraction and halving can be used to calculate the missing side length of a rectangle.
- If you know the perimeter and one of the side lengths you can subtract the known sides and halve the difference.
- Mental and written methods can be used to calculate the perimeter of a 2D shape.
Keywords
Perimeter - The distance around a two-dimensional shape.
Common misconception
Pupils may see a rectangle with the perimeter given and only one of the side lengths and think that there is insufficient information as there are three missing side lengths.
Remind pupils that because it is a rectangle, the side length opposite the given side length is in fact known. A counter can be added on and then removed again to show that they actually know two of the missing side lengths, not just one.
Cycle A uses two-coloured counters to as a means exploring ways to find missing side lengths when the perimeter is known. The Practice tasks are not presented with counters, but including them could be a useful way of scaffolding learning for pupils who are finding the concept challenging.
Teacher tip
Licence
This content is © Oak National Academy Limited (2024), licensed on
Open Government Licence version 3.0
except where otherwise stated. See Oak's terms & conditions (Collection 2).Lesson video
Loading...
Starter quiz
Download starter quiz
6 Questions
Q1.
Complete the sentence. Half of 36 is
Q2.
Which calculations will give the perimeter of this rectangle?
8 + 4
It is impossible to give the perimeter because there are missing side lengths.
Q3.
What is the perimeter of this rectangle?
11 units
16 units
Q4.
What is the perimeter of this rectangle? units.
Q5.
What is the perimeter of this rectangle? units.
Q6.
Order these rectangles from shortest to longest perimeters.
Exit quiz
Download exit quiz
6 Questions
Q1.
The rectangle has a perimeter of 30 units. What is the length of each missing side? units.
Q2.
The rectangle has a perimeter of 20 units. What is the length of each missing side? units.
Q3.
This rectangle has a perimeter of 22 units. The long side of this shape is given. What is the length of each short side? units.
Q4.
A rectangle has a perimeter of 30 units. The long side has a length of 13 units. What is the length of each short side? units.
Q5.
A rectangle has a perimeter of 30 units. The short side has a length of 1 unit. What is the length of each long side? units.
Q6.
Which of these are possible side lengths for a rectangle with a perimeter of 50 cm?
9 cm, 11 cm, 19 cm, 11 cm
10 cm, 10 cm , 10 cm , 10 cm
15 cm, 15 cm, 20 cm, 20 cm