Name: Douglas

Who is asking: Other Level: All

If you know how far around a circle is (say earth) 25000 miles how do you calculate the distance across?


Hi Douglas,

This follow from the wonderful property of circles. No matter how large or small a circle you have, if you divide the distance around (the circumference) by the distance across (the diameter) the answer is always p. That is

 circumference/diameter =

The number is approximately 3.1416 and hence if the circumference is 25000 miles as in your example then  25000/diameter = and the diameter is then  25000/ which is approximately 7958 miles.

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