Testwiki:Reference desk/Archives/Mathematics/2013 October 3

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October 3

PPM?

How much μg Iodine there is in 30ppm Iodine (per 100 g) Iodized salt? Thanks. Ben-Natan (talk) 04:53, 3 October 2013 (UTC)

30 ppm is 30 μg per g, so 3000 μg in 100 g.31.54.112.70 (talk) 11:54, 3 October 2013 (UTC)

This assumes that the parts per million is by mass, as opposed to by volume or count of molecules. StuRat (talk) 11:57, 3 October 2013 (UTC)

True. Typically for solids, ppm, is a concentration based on mass and for liquids, it is a concentration based on volume. Iodised salt indicates the concentrations, at least for those sources, are in terms of mass. --Mark viking (talk) 21:09, 3 October 2013 (UTC)

Interesting. This could possibly cause a strange result where a 1 ppm solid becomes 2 ppm, when dissolved in a liquid. StuRat (talk) 01:16, 6 October 2013 (UTC)

Proof involving binomial

Help please! Can anyone explain the step at 7:10 involving Binomial? Its the only part I don't understand and it's doing my head in!

http://www.youtube.com/watch?v=XHQ0OzqTjd0&feature=c4-overview-vl&list=PL32446FDD4DA932C9 — Preceding unsigned comment added by 31.48.32.249 (talk) 20:50, 3 October 2013 (UTC)

The previous equation (the 6th on that slide), is the Cauchy product and has an error in it. If you listen very carefully (the sound is bad), the speaker mumbles an apology for omitting a factorial sign. It should read

$1=\sum _{n=0}^{\mathrm{\infty }}\sum _{\mu =0}^n\frac{{\mathrm{\beta }}_{\mu }}{\mu !}\frac{1}{(n-\mu +1)!}{s}^n$

--catslash (talk) 22:23, 3 October 2013 (UTC)

Ah i see now! Thanks! That makes so much more sense! Cheers mate! Your a lifesaver! — Preceding unsigned comment added by 81.155.129.116 (talk) 15:02, 4 October 2013 (UTC)