That chart works, of course, but those three particular examples are straightforward. 200 = 100 x 2, so to convert a measurement on 1/200 scale to 1/100 scale, multiply the measurement by 2. 72 = 48 x 1.5, so to convert a measurement on 1/72 scale to 1/48 scale, multiply the measurement by 1.5. 72 = 32 x 2.25, so to convert a measurement on 1/72 scale to 1/32 scale, multiply the measurement by 2.25.
One of the most useful tools for a modern model builder's workbench is an electronic calculator that works in feet, inches, and fractions. Such gadgets used to be rare and expensive, but nowadays you can pick on up at Lowe's or Sears for less than $20.00 - and it probably will have keys to convert between the English and metric systems, too. With a calculator like that, you don't need any theoretical math at all. If you're converting something from 1/72 to 1/48, key the measurement in 1/72 scale into the calculator and multiply by 72. That gives you the size of the real object. Then divide it by 48 to get the dimension in 1/48 scale.
Some people seem to get intimidated by the concept of scale, but it's actually pretty simple. It involves no math beyond basic arithmetic. (I never took a math course beyond high school, and I graduated from high school in 1969. If I can do scale conversions without a table, anybody can.) Just remember that, in working with fractions, the size of the fraction goes down as the denominator (the number on the bottom) goes up. (That is, 1/8 is smaller than 1/4.) As long as the numerator (the number on top) is 1, you can convert from one scale to another by working out the ratio between the two denominators. Figure out in advance whether the result should be smaller or larger than the figure you started with, multiply or divide one denominator by the other (as appropriate), and everything should work out fine.
Part of the problem people have with scale is undoubtedly due to the casual, sloppy way in which some people discuss it. I cringe every time I hear model aircraft builders talk about "quarter scale." A model of even a small aircraft on quarter scale (i.e., 1/4 actual size) wouldn't fit in most people's houses. The perpetrators almost certainly meant "1/4 inch scale," or 1/4" = 1', or 1/48 scale. (There are 48 quarters of an inch in a foot - right?) I wish that phrase "quarter scale" would disappear from the modeling vocabulary. I've never heard anybody refer to a model on 1/72 scale as "sixth scale" - which would make just as much sense.
I apologize if this as insulted anybody's intelligence. An understanding of scale is pretty fundamental to scale modeling, and I get uncomfortable when I see anybody get intimidated by it.