Working out the Perimeter of Plane Figures - Grade 4 Math

What is the perimeter of the figure below?

Perimeter is calculated by adding all the sides of the square.
Remember that all sides of a square have equal measurements
So, if One side is marked 10 cm, all sides are 10 cm
Perimeter = L + L + L + L or L x 4
= 10 + 10 + 10 + 10 (or 10 x 4) = 40
= 40 cm (do not forget the units)

What is the perimeter of the figure below?

Perimeter is calculated by adding all the sides of the Rectangle.
Remember that two opposite sides of a rectangle have equal measurements
So, if One side is marked 10 cm, the opposite side is also 10 cm.
Perimeter = L + W + L + W or (L x 2) + (W x 2) or 2L + 2W
= 18 + 10 + 18 + 10 or (18 x 2) + (10 x 2) = 56
= 56 cm (do not forget the units)

What is the perimeter of the figure below?

Perimeter is calculated by adding all the sides of the shape.
Draw the shape on a paper and mark each side when you add it. This will help prevent adding a side twice.
= 12 + 7 + 16 + 10 + 18 = 63
= 63 cm (do not forget the units)

When working with metres and centimetres, always remember:

Example 2.1

Convert 16 metres to centimetres

Remember 1m = 100 cm
Hence,
16 m = ? cm
16 x 100 = 1600 cm.
1600 cm

Example 2.2

Wok out

Answer

Example 2.3

Mary's drew a 1m and 30 cm line on the sand. John's drew 5m and 10 cm from where Mary left. How long was the line?

Answer

Example 3.1

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Answer

Example 3.2

A stick measured 3m and 16 cm. Mercy cut 1m and 50 cm from it. What was length of the remaining stick.

In this example, 16 is less than 50 and hence will leave a negative number. Hence, we 'borrow' 1 metre from the metres column, convert it to centimetres and add 16. It will be 116.
Therefore, 116 - 50 = 66.
On the metres column, we are left with 2 - 1 (remember we 'borrowed' 1m earlier)
2 - 1 = 1

Example 4.1

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Answer

First, we multiply 40 by 3 to get: 40 x 3 = 120
Remember that 100cm = 1, hence the 120cm can be converted to metres to give 1m and 20cm
Write the 20 in the cm column and 'carry forward' the 1m.
Then multiply 2 x 3,
2 x 3 = 6,
Then add the 1 we had 'carried forward' earlier,
6 + 1 = 7m,
Hence the answer is 7m 20cm.

Example 5.1

Wok out

Answer

Your answer, 6m 9cm.