Wednesday, August 8, 2012

More Integer Operations


I was writing this in another person's blog entry about rules for integers. Figured I might as well put it on my blog.

For subtracting, I like to talk about owing money. If you’re at the restaurant, and you have a bill for $45 (-45), and I come along and say, “Hey, let me pay that for you.”, I would take away that negative: -45 – (-45) = 0. You now owe nothing.

You can do similar things for multiplying.
3(5) means I give you three 5 dollar bills: net result, add 15 (+15)
3(-5) means I give you three IOU slips (each owing $5): net result, lose 15 (-15)
-3(5) means I take away three of your 5 dollar bills: net result, lose 15 (-15)
-3(-5) means I take away three IOU slips: net result, gain 15 (+15)
OR
getting something good is good
getting something bad is bad
losing something good is bad
losing something bad is good
I learned that last one from a student, and who knows where he picked it up.
Nathan Kraft

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