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Q&A #19441


Approximations of pi

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From: Gail (for Teacher2Teacher Service)
Date: Mar 30, 2008 at 07:45:29
Subject: Re: Approximations of pi

Hi Ashley,

Rather than thinking about which is more accurate, I try to help my students
think about which of the approximations they should use for Pi in each
circumstance.  For example, if they are working with a problem where the
given dimension of the circle, either the radius or the diameter, is a
multiple of 7, it is easier to use 22/7, because when you begin to multiply,
the denominator will "cancel out". Like this:

Find the circumference of a circle with a diameter of 14 inches:

C = 22/7 x 14   or (22 x 14)/(7 x 1).  The 14 and the 7 become 2/1, so you
have (22 x 2)/(1 x 1), which is just 44, so the answer is 44 inches.

If you did that same problem using 3.14 instead of 22/7, you would end up
with C = 3.14 x 14, which is 43.96 inches.

I hope this gives you something to think about.

 -Gail, for the T2T service

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