Math worksheet for finding missing sides of rectangles using perimeter.

Let’s solve each problem one by one. Remember: for a rectangle, opposite sides are equal. So if you know one side and the perimeter, you can find the missing side.

The formula for perimeter of a rectangle is:
Perimeter = 2 × (length + width)

We can rearrange this to find a missing side:
If we know the perimeter and one side, then:
→ Add the two known sides (they’re equal on opposite sides)
→ Subtract that from the total perimeter → that gives you the sum of the other two sides
→ Divide by 2 → that’s the length of one missing side

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Problem 1:
Given: One side = 40 mm, Perimeter = 130 mm
The two long sides together = 40 + 40 = 80 mm
So the two short sides together = 130 - 80 = 50 mm
One short side = 50 ÷ 2 = 25 mm

✔ Check: 2×(40 + 25) = 2×65 = 130 → Correct!

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Problem 2:
Given: One side = 2½ cm, Perimeter = 16 cm
First, write 2½ as 2.5 or keep as fraction — let’s use fractions: 2½ = 5/2
Two of these sides = 5/2 + 5/2 = 10/2 = 5 cm
Remaining for the other two sides = 16 - 5 = 11 cm
One missing side = 11 ÷ 2 = 5½ cm

✔ Check: 2×(5½ + 2½) = 2×8 = 16 → Correct!

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Problem 3:
Given: One side = 6 cm, Perimeter = 38 cm
Two of these sides = 6 + 6 = 12 cm
Remaining = 38 - 12 = 26 cm
One missing side = 26 ÷ 2 = 13 cm

✔ Check: 2×(6 + 13) = 2×19 = 38 → Correct!

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Problem 4:
Given: One side = 6½ m, Perimeter = 22 m
6½ = 13/2
Two of these = 13/2 + 13/2 = 26/2 = 13 m
Remaining = 22 - 13 = 9 m
One missing side = 9 ÷ 2 = 4½ m

✔ Check: 2×(6½ + 4½) = 2×11 = 22 → Correct!

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Problem 5:
Given: One side = 12 mm, Perimeter = 84 mm
Two of these = 12 + 12 = 24 mm
Remaining = 84 - 24 = 60 mm
One missing side = 60 ÷ 2 = 30 mm

✔ Check: 2×(12 + 30) = 2×42 = 84 → Correct!

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Problem 6:
Given: Perimeter = 18 m, but no side given? Wait — look again. The diagram shows it’s a square? No — actually, in the image, all angles are right angles, but only one side is labeled with a blank. But wait — maybe it’s a square? Let me check.

Actually, looking back — in problem 6, there’s NO side given at all? That can’t be. Wait — perhaps I misread.

Wait — re-examining: In problem 6, the rectangle has no side labeled except the blank. But perimeter is 18 m. Hmm… unless it’s a square? But the title says “rectangle”, not necessarily square.

Wait — hold on! Looking at the original image description — in problem 6, it’s drawn like a square, but still called a rectangle. However, without any side given, we can’t solve it — unless... did I miss something?

Wait — no, actually, in the user’s image, problem 6 might have been intended to be a square? Or maybe I made a mistake.

Wait — let me double-check the original problem list:

Looking back: Problem 6 says “Perimeter = 18 m” and asks for one side, with no other side given. That would only work if it’s a square.

But the worksheet says “rectangle”, so unless specified, we can’t assume square.

Wait — perhaps in the actual image, problem 6 has a side labeled? Let me think — since the user provided an image, and in my initial analysis I didn’t see a side, but maybe I missed it.

Wait — no, in the text description above, for problem 6, it just says “______ m” and “Perimeter = 18 m”. No other number.

That suggests it might be a square? Because otherwise, infinite solutions.

But the worksheet title is “PERIMETER OF A RECTANGLE MISSING SIDES 2”, implying rectangles, not necessarily squares.

Wait — perhaps in the image, problem 6 is actually a square? Many worksheets do that — show a square but call it a rectangle (which is technically correct).

Given that, and since no side is given, the only way to solve is if it’s a square.

So assuming it’s a square (all sides equal):

Perimeter = 4 × side → side = 18 ÷ 4 = 4.5 m = 4½ m

✔ Check: 4 × 4.5 = 18 → Correct.

Alternatively, if it’s not a square, we can’t solve — but since it’s a homework problem, likely intended to be a square here.

In many such worksheets, when only perimeter is given and one blank side, and shape looks square, they mean square.

So I’ll go with 4½ m

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Final Answers:

1) 25 mm
2) 5½ cm
3) 13 cm
4) 4½ m
5) 30 mm
6) 4½ m

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Final Answer:
1) 25 mm
2) 5½ cm
3) 13 cm
4) 4½ m
5) 30 mm
6) 4½ m