Inv 2.2 Subtracting of intergers.

Answers to page 45 ACE #18-29 - Answers Found here.

Subtraction of integer strategies:

• Students may already see that you can change a subtraction expression to addition by adding the opposite of the second number.

• Some may realize that when you are subtracting, you will get a positive answer if the number you start with is greater than the number you subtract. For example, $17$ + − 15 + , $17$ + − 1 − , and $15$ − − 21 − all give positive results. You will get a negative answer if the number you start with is less than the number you subtract. For example, $13$ + − 1 + 5 , $1$ − − 1 + 5 , and $1$ − 5 − 1 − 3 all give negative results. To find the value of the answer, you find the difference of the numbers.

• Some students will think in terms of four sub-categories.

  • $P$ o s i t i v e − P o s i t i v e = P o s i t i v e if the number you start with is greater than the number you subtract and negative otherwise.

  • $P$ o s i t i v e − N e g a t i v e = P o s i t i v e

  • $N$ e g a t i v e − N e g a t i v e = P o s i t i v e if the number you start with is greater than the number you subtract and negative otherwise.

  • $N$ e g a t i v e − P o s i t i v e = N e g a t i v e