Missing sidePerimeter given
Name: Date:
Find the missing side. All lengths are in centimeters.
1 cm
2 cm
3 cm
4 cm
5 cm
6 cm
7 cm
8 cm
Find a side from the perimeter worksheets
A rectangle's perimeter is the two sides doubled, so halving it gives back the length plus the width — and one subtraction finishes the job. These free printable worksheets run the perimeter formula backward, every figure marked with P.
Kid stuck on one? You don’t just get the sheet.
Find a side from the perimeter
The answer key prints on a separate page.
What's on this sheet
The mixed missing-side sheets ask a child to tell area from perimeter first; this one is perimeter throughout, so the method is the same two steps every time. Halve the perimeter to get the sum of one length and one width, then subtract the side you were given — and doing that repeatedly is what builds the two-step move before it is set against division on a mixed page.
Why this sheet works
The step children skip is the halving. A perimeter is four sides, not two, so subtracting a known side straight from the whole perimeter leaves far too much; the halve has to come first, which is exactly why the figure prints P rather than a bare number.
How this one works
One question from this sheet, worked through a step at a time.
Missing side: perimeter 56, one side 8
2 × (8 + ?) =56
56 ÷ 2 =28
56 ÷ 2 =28
28 − 8 =20 cm
- Forwards, the perimeter goes round twice: 56 is 8 + ? + 8 + ? — each side counted two times.
- So undo the doubling FIRST: half of 56 is 28, and that is one long side plus one short one. Taking 8 off the whole 56 is the natural wrong move — it forgets that 8 is in there twice.
- Now take the side you know off that half: 28 − 8 = 20 cm.