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 Everyday Examples
 Pi:  The ratio of the circumference of a circle to its diameter.
When planes fly long distances, they are actually flying in the path of an arc of a circle. The path must be calculated in order to accurately predict how much fuel to use. The number Pi must be used to calculate the arc length.

A plane flies in an arc.  Pi is needed to calculate the distance.

Pi must also be used to find the area of any circle or the volume of any sphere. For example, Pi must be used to calculate the volume of the moon.

The moon is a sphere, and the number pi is necessary to calculate the volume of a sphere.