Please Lie More Carefully

I’m not saying textbook problems have to use real-world data. In fact, as far as I’m concerned, there’s way too much emphasis on “applications” in college maths (and below). But.

For heck sake, when you make stuff up, do it carefully enough that it isn’t obviously impossible. I’ve just come from working with a statistics student. We were supposed to test the claim that a certain population proportion was 10% against a sample proportion of 13%, based on n= 57 data points (at some stated confidence level that I’ve forgotten). But wait a minute. You can’t get 13% from a sample of 57 subjects: {7\over{57}}\sim .122807 (i.e., 12%) and {8\over{57}}\sim .14035 (i.e., 14%). Now, this is from a textbook. You should see some of the nonsense the actual instructors make up. And what I am saying is: quit telling stupid lies. Or become an administrator or something.

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  1. The old story favored in southern Idaho, where a lot of people ran sheep, is the old story problem about 20 sheep in a pen, and one jumps out. “How many sheep are left in the pen?” the first-year, fresh out of city college teacher asks. “None,” Johnny replies.

    “No, Johnny, that’s wrong. You don’t know your math.”

    “Oh, I know math, Ms. Smith — you don’t know sheep!”

    In one of my credit recovery economics classes I had a kid who didn’t think he understood economics and who hated the math. A day after he learned his girlfriend was pregnant, he told me he found a good set of “clean rims” (fancy wheels). They’d set him back only $800.00, but they were worth more, he said.

    So I had him calculate the value of that $800.00 in 18 years, when his kid was ready to enter college. Then I had him calculate the value in 47 years, when he was ready to retire.

    Real world, real problems — he told me a week later he hadn’t bought the wheels, and he wondered how to get close to the 10% return he wanted. Real problems produce real solutions.




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