If you know the area and one side, the other side is a missing factor.
Step 1: Let's Learn
Read it, or press Listen and follow the words.
An example
An area of 24 with a side of 6. What times 6 makes 24? The other side is 4.
Or divide
24 ÷ 6 = 4. It is the same question either way.
Working backwards from the area
If a rectangle has an area of 24 square centimetres and one side is 6, the other side is 24 ÷ 6 = 4. Area is a multiplication, so finding a missing side is a missing-factor problem — the same structure you met in Chapter 3, now wearing a geometric costume.
Multiply back to check
6 × 4 = 24, which matches the given area, so the answer is right. Checking by multiplying is quick and independent of how you found the answer.
Several rectangles can share an area
An area of 24 could come from 1 × 24, 2 × 12, 3 × 8, or 4 × 6. Knowing only the area does not fix the shape. That is why the problem must give you one side — and it is a first taste of how many different shapes can hide behind a single number.
Step 2: Try It Yourself
Tap and try it out.
Area · squares inside
24
Perimeter · walk around
20
6 × 4 = 24 · 6 + 4 + 6 + 4 = 20
Area counts the squares inside. Perimeter measures the walk all the way round.
Step 3: Watch an Example
One step at a time.
Watch Ana Work Backwards
Ana has a rectangle with an area of 35 and one side of 5.
- Step 1
She writes what she knows: 5 × ? = 35.
Step 4: Your Turn
Practice makes it stick.
The Garden Bed
Problem 1 of 2
A bed has an area of 32 square metres and is 4 metres wide. How long is it?
metres
The Sticker
Problem 2 of 2
A sticker has an area of 18 square cm and is 3 cm tall. How wide is it?
cm
Find the Missing Side
1 of 3
Area 24, one side 6. What is the other side?
2 of 3
Area 45, one side 9. What is the other side?
3 of 3
Area 56, one side 7. What is the other side?
Step 5: Quick Check
Show what you know.
Question 1 of 2
Area 42, one side 6. What is the other side?
Question 2 of 2
What kind of question is finding a missing side?
What You Learned
- Area is one side times the other.
- A missing side is a missing factor.
- Divide the area by the side you know.