Date: Wed, 15 Jul 1998 03:07:26 +0300
From: Bonnie Warmund Teboul
When I learned this rule I was convinced that I would prove my teacher wrong.
Some where in college I finally convinced myself that it really does make sense!!
Try a chart 3x10
0 = 300 -3x 100= -300
3x 10 = 30 -3x 10= -30
3x 1 = 3 -3x 1= -3
3x 0 = 0 -3x 0= 0
3x -1 = -3 -3x -1= ?
3x-10 = -30 -3x -10= ?
... ...
Follow the progression and you can easily understand what is happening without mirrors.
As we multiply a positive number by progressively smaller numbers the answer gets progressively smaller. When we multiply a negative number by progressively smaller numbers the answer becomes progressively bigger! (because it is less negative)
If you want a practical example, try thinking of a bank account. Say you deposit $20 a month then
3 months in the future you have +3 x +$20 = +$60 (more than today) 3 months ago you had -3 x +$20 = -$60 (less than today)
Now say you withdraw $20 a month then
3 month in the future you have +3 x -$20 = -$60 (less than today) 3 months ago -3 x -$20 = +$60 (more than today)
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