Missing side length, step by step
Knowing that area is length times width is one thing.
The question
cm
Missing side: area 50, one side 10
10 × ? =50
× is undone by ÷
50 ÷ 10 =5 cm
check: 10 × 5 =50
- Forwards, area is one side times the other: 10 × ? = 50. Every number you need is here, which is exactly why the usual mistake is to multiply them.
- But the 50 is the ANSWER to that multiplication, not another side. To get back to the missing one, undo the multiply — and the undo of multiplying is dividing.
- 50 ÷ 10 = 5 cm. Check it forwards: 10 × 5 = 50, which is what the question said.
How it works.
- 01
Forwards, area is one side times the other: 10 × ? = 50. Every number you need is here, which is exactly why the usual mistake is to multiply them.
- 02
But the 50 is the ANSWER to that multiplication, not another side. To get back to the missing one, undo the multiply — and the undo of multiplying is dividing.
- 03
50 ÷ 10 = 5 cm. Check it forwards: 10 × 5 = 50, which is what the question said.