Find the diameter

The circumferenceof a plate is 31”

2πr = circumference

Find the diameter2πr = 312πr = 312π = 2π

6.28r = 316.28 = 6.28Diameter of plate is 10”

Radius of plate is 5”

Find the diameter

The circumference of bottom of cupcakeIs 6.5”

2πr = circumference

Find the diameter2πr = 6.52πr = 6.52π = 2π

6.28r = 6.56.28 = 6.28

Diameter of cupcake is 2”

Radius of cupcake is 1”

Find the diameter

The circumference of top of a mugis 13”

2πr = circumference

Find the diameter2πr = 132π = 2π 2πr = 13

6.28 = 6.286.28r = 13

d = 4”

r = 2”

Find the diameterThe circumference of wheelis 314 cm

2πr = 3142π = 2π 2πr = 314

6.28 = 6.28

2πr = circumference6.28r = 314d = 100cm

r = 50cm

Find the diameter

The circumference of the top of a water pail is 100 cm

2πr = 1002π = 2π 2πr = 100

r = 16cm

6.28 = 6.28

2πr = circumference

2πr = 100d = 32cm

Find the diameter

The circumference of the earth is 24,901 miles

2πr = 24,9012π = 2π 2πr = 24,901

r = 3965

6.28 = 6.28

2πr = circumference2πr = 24,901

d = 7930

A circle with radius 3 cm is enlarged so its radius is now 6 cm

Draw a figure to represent this idea

By what scale factor did the circumference increase?

2π(3) = c6.28(3) = cc = 19

2π(6) = c

6.28(6) = cc = 38

By what scale factor did the area increase?

π(3)(3) = a3.14(9) = a28cm = a

π(6)(6) = a

3.14(36) = a113cm = a

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