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How do you use pi to find the area and circumference of a circle?

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Ex: 3.14x23x23=1,661.06
C=pi x diameter OR 2 x pi x radius
Ex: 3.14x36=113.04
2x3.14x36=113.04
With circumference, both formulas get the same answer. Here's a trick: If you are given the diameter, use pi x diameter. If you are given the radius, use 2 x pi x radius.

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Area = pi(r^2),
Circumference = 2pi(r)

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1. Brady buys 2 notebooks and should get \$3 back in change. The cashier gives him 12 quarters. Determine if Brady was given the correct amount of change.
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How many quarters are in \$3.00?
There are 4 quarters in \$1.00.
4 x 3 = 12 quarters in \$3.00.
So he got exactly the right change.
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claire7752 is correct
another way to find circumference is: pi(d)

d = diameter

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Thanks Izzugardo.
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Pi, which is 3.14 (rounded) can be used to find the diameter by doing 3.14 times the diameter. To find the circumference, you do pi times the radius squared.

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Close,.but not completely correct.
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