My Math Forum 1000 times wrong!

 Elementary Math Fractions, Percentages, Word Problems, Equations, Inequations, Factorization, Expansion

 March 15th, 2014, 05:47 PM #1 Newbie   Joined: Mar 2014 Posts: 2 Thanks: 0 1000 times wrong! Okay, this is probably straight forward but I don't know it so please help. My problem, which I'm sure you will have come across, is with magnitude. In particular the unit which my answer is returned in. In my problem on area of a circle: radius = 4 mm Area of circle = ? r^2 So: Area = ?.4^2 = ?.16 = 50.265 mm^2. Easy. But if I use standard form 4 mm becomes 4 x 10^-3 m with the below result: Area = ?.(4 x 10^-3)^2 = ?.(1.6 x 10^-5) = 5.0265 x 10^-5 m. Now this reads 50 nano metres which is wrong, 1000 times wrong! So how do I get my calculator to display the right value? Do I just need to manually disregard three 0's or is there a better way?
 March 15th, 2014, 08:16 PM #2 Math Team     Joined: Jul 2011 From: North America, 42nd parallel Posts: 3,372 Thanks: 233 Re: 1000 times wrong! You forgot to square the meter , $\text{Area} \= \ \pi(4 \cdot 10^{-3} m)^2 \ = \ 5.0265 \times 10^{-5} \ m^2$ Now , if you make the substitution , $1 \ m^2 \= \ 10^6 \ mm^2$ Everything will check out.
 March 16th, 2014, 08:45 AM #3 Newbie   Joined: Mar 2014 Posts: 2 Thanks: 0 Re: 1000 times wrong! Damn right it does Agent Redlum! Thanks

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