This is one of my pet peeves too:

Percentage Points

People often think that if you decrease something by 50% then increase it by 50% you end up with the original value. It’s surprisingly difficult for people to grasp this is not true. I found it works better if you use 100% reduction followed by a 100% increase. When they say, “But that is different.” I just walk away to avoid the nearly irresistible urge to do some minor cleaning of the gene pool.

8 thoughts on “Percentages

  1. Ugh… the stupid percent thing. I always end up explaining it as $100 take 10%, then add 10%. 100 – 10% = $90. Add 10%, and you get $99.

  2. You’d be surprised how many people who were flipping houses didn’t get the percentage thing. They never understood it was 100% on the way up but it only took 50% down to get to the same place. Duh.

    Another thing that gets me is the people who are *dazzled* by percentages. It really makes a big difference if you start off with a base of 1 versus a base of 100,000. It’s fantastic that sales are up 300% but you have to look at the base number to determine if that is really a tremendous increase or not.

  3. When Richmond was going to impose a regional tax increase on Northern Virginia I did my best.
    The tax RATE was going from 4.5% to 5%.
    “It’s only going up 1/2 a percent …” said the publicly educated.
    I’d slowly explain that it was really an 11.1% increase.
    Once the increase, which was on a ballot referendum, failed the governor closed the 3 of the 5 busiest DMV offices in NoVA.
    The next year the whole state received a tax hike to 5%.

  4. Ask your average high school graduate how to calculate their home state’s sales tax (the price of a taxed item is x and the tax rate is y. What’s the total?)

    We’ve hired several college accounding majors. Not one of them could back the sales tax out of a total to arrive at the selling price.

    Public schools have done their work very well.

  5. Didn’t we learn this in the fourth grade? I mean, I never learned calculus and diffy-q properly, and promptly forgot what little I learned, but things learned when a little kid tend to stick with one forever.

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