Tuesday, September 10, 2013

Multiplying Incorrectly

It was the second day of school. I was just getting first period started when Mr. Claus arrived. He informed me that he was going to be the instructional assistant for the class.

I have worked with Mr. Claus in the past. I've subbed for the teacher he's usually paired with, and he's also been the IA in other classes I've covered. So, when he arrived I nodded and gave him a copy of what we were working on.

Mr. Claus is not his real name. When telling school stories, I don't use real names. But Mr. Claus is a very fitting alias for the man. I'm sure you have a pretty good image of what he looks like in your head right now.

The class was a CAHSEE math prep class. It's a class students who failed the math portion of the CAHSEE are required to take. Turns out, half the students are special ed, so that's why an IA was assigned. Score!

I was demonstrating some math questions for the class. It was a question involving percents. We were supposed to calculate 40% of $125. So, I wrote out the question, did the multiplication, came up with $90...

Mr. Claus spoke up. "I don't think that answer is correct."


Mr. Claus then went on to explain to the class that while working out problems, the students should take note of whether or not their answers make sense. Since $90 is over half of $125 and the question asked for 40% which is less than half, that answer doesn't make sense.

The arithmetic gets me every time. And then I almost forgot the second half of the question--to find the sale price after the 40% was taken off.

Well, at least I demonstrated how to not do the problem...


  1. The human brain absolutely sucks as a calculator.

  2. Oops. That's something I'd do. It's been interesting teaching my 12 yr old Algebra and now Geometry. Thankfully we're not stumbling through too badly.


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