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• Nige #1 - Comment permalink August 12th, 2010 at 08:46

  This is the thing. Dilutions. Be it cells or drugs, this hurdle is one of the biggest, simple, early problems that any lab scientist faces. I remember learning it in Pharmacology 3.1.4 at Aberdeen, and later, I remember teaching it in Pharmacology classes at Liverpool. In the end, I used to use a method that involved working out the single, massive dilution factor needed, and then breaking it down into serials. Certainly, that was the easiest way to teach it.

• Jenny #2 - Comment permalink August 12th, 2010 at 08:54

  I was pretty amazed when Alan worked out that if you put your desired concentration and your current concentration into the same scientific notation (e.g. 1 x 10^6 and 345 x 10^6) then you could disregard the 10^6 altogether. But I actually use your method (the nested serials). Probably the most important math thing I ever learned was that you can guesstimate the ballpark using common sense, and then use this figure to ensure that you haven’t done something drastic like drop a decimal somewhere.

• rwintle #3 - Comment permalink August 13th, 2010 at 01:29

  My grade 13 chemistry teacher, a Mr. Caskey, taught us the very useful “Caskey Conversion”. Used when converting micrograms/microlitre into grams/litre. It’s stayed with me to this day.

  I mention this as it seems peripherally related to Alan’s disregarding of many orders of magnitude all at once. Well done that lad.

• Jenny #4 - Comment permalink August 13th, 2010 at 08:49

  I think I might have learned something similar – is that when you line up all the ratios and everything crosses out diagonally except the x per y units you’re trying to arrive at?

• rwintle #5 - Comment permalink August 13th, 2010 at 15:52

  Um, I suppose you could make it that complicated… this is just a “multiplication by 1″.

  I *loved* those “units analysis” problems where all the extraneous moles and mLs and things disappeared…

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