Page 78 - MarceAlgebra Demystified

CHAPTER 4

Negative Numbers

A negative number is a number smaller than zero. Think about the readings
on a thermometer. A reading of 108 means the temperature is 108 below 08
and that the temperature would need to warm up 108 to reach 08. A reading
of 108 means the temperature would need to cool down 108 to reach 08.
Let us use a test example to discover some facts about arithmetic with
negative numbers. Suppose you are taking a test where one point is awarded
for each correct answer and one point is deducted for each incorrect answer.
If you miss the first three problems, how many would you need to answer
correctly to bring your score to 10? You would need to answer three cor-
rectly to bring your answer up to zero, then you would need to answer 10
more correctly to bring your score to 10; you would need to answer 13
correctly to bring a score of 3 to 10: 10 ¼ 3 þ 3 þ 10 ¼ 3 þ 13. Now
suppose you miss the first eight problems and get the next two answers
correct. You now only need to answer six more correctly to reach zero:
8 þ 2 ¼ 6.
When adding a negative number to a positive number (or a positive num-
ber to a negative number), take the difference of the numbers. The sign on
the sum will be the same as the sign of the ‘‘larger’’ number. If no sign
appears in front of a number, the number is positive.

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