# Percentages

This is one of my pet peeves too:

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. This is why financial reports are in BPS, or Basis Points. Too bad they’re universally called “points”; reading the Investopedia entry made me cry.

5. 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.

6. 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.

7. Ry, here in FL, the equation would be: x=0.06y+y. Solve for y. Y=x/1.06. We learned that kind of thing when we were 14, right?

8. Sorry, my last should have been addressed to Lyle.