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by Peter Moskos

October 7, 2014

After a 200-percent decrease in basic math skills...

As promised, here is how to determine basic percentages. Too many of my college students don't understand basic percentages. Clearly GTF has the same problem. So here is how it works -- in words -- with no math symbols. I'm totally serious. It's never too late to learn. And not knowing how to relate "doubled" and "100% increase" is the mathematically equivalent of being functionally illiterate.

To say how many times something increased, simply divide the second number by the first: There were 10 arrests; now there are 30. 30 divided by 10 is 3. Arrests tripled.

To figure out a percent increase or decrease, subtract the first (earlier) number from the second (later) number and then divide the result by the first number (multiply by 100 -- move the decimal place over two to the right -- to get a percentage).

30 minus 10 is 20; 20 divided by 10 is 2; 2 times 100 is 200. So 30 arrests is a 200 percent increase compared to 10. A 100 percent increase would be the same as saying something doubled.

Going the other way, from 30 to 10 arrests would be one-third as many arrests or a two-thirds decrease or a decrease of 67 percent.

And nothing, not even math skills, can decrease more than 100 percent.

Next I'm going to talk about rates.

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