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1. The problem statement, all variables and given/known data

if the inner radius of a ring is 3,56 cm and the outer radius is measured as 3,32 cm, compute the area of the ring

2. Relevant equations

When multiplying the number of significant figures stays the same, when adding or subtracting we keep same number of decimals.

Area of a circle: \pi r^2

3. The attempt at a solution

I'm basically subtracting [itex]\pi r_1^{2}-\pi r_2^2[/itex]. When squaring the radii I get three significant figures and when subtrating I keep two decimals. The answer that way has two decimals for a total of three significant figures, my answer would be [itex]\pi 1.65 cm^2[/itex] (pi has infinite significant figures). However, if I rearrange the formula as [itex]\pi (r_1+r_2)(r_1-r_2)[/itex] for [itex]r_1-r_2[/itex] I get 0, 24 cm which only has two significant figures, this crops the total number of significant figures down to two when multiplied with [itex]r_1+r_2[/itex]. What am I doing wrong?

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# Homework Help: Significant figures ambiguity

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