When I was a kid, I was taught to memorize that:
pos times pos is pos
neg times pos is neg
pos times neg is neg
neg times neg is pos
So I memorized it. And over time I came to understood why that was the case.
But I didn’t want my students to just memorize it. So on Thursday, and then again on Friday to reinforce, I gave my students green and yellow chips. We talked about poker chips representing money and debt and gambling. That was easy enough. Then we made each chip represent $5. Green was +5 and yellow was -5. Getting/gaining a chip was positive. Losing/giving away a chip was negative.
Gain four green chips. I just gained $20.
4 * 5 = 20
Lose four green chips. I just lost $20.
-4 * 5 = -20
Gain four yellow chips. I just lost $20.
4 * -5 = -20
Lose four yellow chips. I just gained $20.
-4 * -5 = 20
And the students got it.
Sometimes teaching is so exciting.
I’ve realized that I need to give these students very, very frequent tests and quizzes to make sure that they understand the math we’re doing. They don’t want to ask for help because they’re so used to being “the smart ones.” And we study at a quicker pace than the elementary curriculum. (In less than two weeks we learned about negative and positive integers, absolute value (an eighth grade objective), and adding, subtracting, multiplying and dividing like and unlike integers. It takes one week or more in sixth grade just to do positive and negative integers.) I’m glad I realized this during the first quarter rather than later in the year.
Subatomic, taking a test: Ms S, did you make this test? Because number three is already in order from greatest to least.
Amanda Teacher, smiles: You just told everyone else the answer.
Dead Meat, deadpan voice: Yeah, man, thanks for ruining our mojo.