Sig figs & averaging

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From: Geoff Ruth (gruth@uclink4.berkeley.edu)
Date: Thu Sep 28 2000 - 14:26:45 PDT 

Message-Id: <v04011709b5f967430819@[128.32.190.180]>
Date: Thu, 28 Sep 2000 13:26:45 -0800
From: Geoff Ruth <gruth@uclink4.berkeley.edu>
Subject: Sig figs & averaging

I've been thinking about significant figures a lot recently, and
contemplating when scientists do and don't use them. Here's a simple
example.

If you had two objects with masses of 2 g and 3 g, and you wanted to find
their average, I think that most chemists would report the average mass as
2.5 g. But according to sig fig rules, their average mass should be 3 g.
That seems slightly insane to me: the idea of averaging 2 g and 3 g to get
3 g is very weird to me, as well as my students.

Advice?

-Geoff Ruth
Leadership High School
300 Seneca Avenue
San Francisco, CA 94112

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