Why Do Two Negatives Equal a Positive?Date: 6/6/96 at 0:10:45 From: khan munir Subject: Integers + and - Dr. Math, Please explain the use of integers + and - . I don't understand why two (-) = the +. Thank you, kmunir Date: 6/21/96 at 15:47:19 From: Doctor Leigh Subject: Re: Integers + and - Perhaps the best way to think about integers and positive and negative adding is using two different objects, one which represents positive and one which represents negative. For this explanation let's use pennies and dimes. A penny will represent a -1 and a dime will represent a +1. Take a piece of paper or create a space so that we can do the addition and subtraction. Divide it into two sides - one for pennies (negatives) and one for dimes (positives). Now let's talk about addition and subtraction. When we add something we will increase the number of pennies or dimes by one depending on what we are adding (a negative or a positive). When we subtract we will decrease the number of pennies or dimes by one depending on what we are subtracting (a negative or a positive). Let's start with 5 pennies on the negative side and 5 dimes on the positive side. This will give us a zero balance (-5 + 5 = 0). Let's add a positive 3 to our "pot". if you add up both sides you should get a 3 now. (-5 +8 = 3) Now take the positive 3 away so that both sides are even again. Subtract a negative three from the pot. (Take three pennies out of the negative side.) Now add up your pot. The negative side is now -2 and the positive side should be 5. You should get a positive 3. Try adding and subtracting other positive and negative numbers. Your results should be the same. I hope I demonstrated to you why two negatives make a positive. Thank you for your question. -Doctor Leigh Ann, The Math Forum Check out our web site! http://mathforum.org/dr.math/ |
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