1. If you write out pi to two decimal places, backwards it spells "pie".

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3.14 = PIE.

2. A French word for pie chart is "camembert".

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Because of course it is.

3. The spiral shapes of sunflowers follow a Fibonacci sequence.

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That's where you add the two preceding numbers in the sequence to give you the next one. So it starts 1, 1, 2, 3, 5, 8, 13, 21, etc. The Fibonacci sequence shows up in nature a fair bit.

4. The Fibonacci sequence is encoded in the number 1/89.

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1/89 = 0.01 + 0.001 + 0.0002 + 0.00003 + 0.000005 + 0.0000008 + 0.00000013 + 0.000000021 + 0.0000000034 etc.

5. A pizza that has radius "z" and height "a" has volume Pi × z × z × a.

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Because the area of a circle is Pi multiplied by the radius squared (which can be written out as Pi × z × z). Then you multiply by the height to get the total volume.