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**The Perimeter Of A Shape.**

Regular Octagon 6cm 4cm 5cm 3cm

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The Idea Of Perimeter. Perimeter is the distance around the outside of a shape. What is the perimeter of the shapes below ? (2) 5.6m 8.9m (1) 6cm 4cm P = 6 + 4 + 6 + 4 P = 2 x ( ) P = 20cm P = 29m

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(3) 5cm 3cm 4cm (4) 10m Regular Octagon P = 3 + 4 + 5 P = 12cm P = 8 x 10 P = 80 m

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**What Goes In The Box ? Calculate the perimeter of the shapes below:**

(2) 9.7cm 11.4cm (1) 9 cm 4cm P = 26cm P=32.5cm (3) 7.8 m 10.3m 8.1m 7.9m (4) 12cm P = 34.1m P=72cm

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**The Perimeter Of A Circle.**

Look at the circle below: Circumference. What do we call the distance around the circle? What do we call the distance across the circle ? Diameter Key Question. How many times bigger is the diameter of the circle compared to the diameter ? The circumference is a bit more than three times the diameter.

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**Estimating The Circumference.**

If we know that the circumference of a circle is roughly three times the diameter , then estimate the circumference of the circles below: (2) 9m (1) 6cm Circumference = 3 x diameter C = 3 x 6cm Circumference = 3 x diameter C = 3 x 9m C = 18 cm C = 27m

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The Number Called Pi. After a great deal of measuring and calculating , Greek mathematicians came up with a better estimate of how many times bigger the circumference was compared to the diameter. Key Fact. They found that the circumference was 3.14 times bigger than the diameter. They called 3.14 Pi after a letter in the Greek alphabet. The letter pi is written as : The Circumference Of A Circle. Circumference = Pi x Diameter

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**Calculating The Circumference.**

Calculate the circumference of the circles below: (2) 2.8cm (1) 10m C = x D C = x D = 3.14 D = 10m = 3.14 D = 2.8cm C = 3.14 x 10 C = 3.14 x 2.8 C = 31.4m C = 8.8cm

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What Goes In The Box 2 ? Calculate the circumference of the circles shown below: (1) 4cm (2) 26cm 12.6cm (3) 2.3m 81.64m 14.4m

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**Perimeter Of More Complex Shapes.**

Calculate the perimeter of the shapes below: (1) 12m P = D + ( D) 2 P = 12 + (3.14 x12) 2 P = P = cm

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(2) 10 m 8 m P = 10 + 16 + (3.14 x10 2) P = 26 + 15.7 P = 41.7m

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(3) 10cm P = 10 + 10 + (3.14 x 20) x 0.75 P = 20 + 47.1 P = 67.1 cm

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