3) 12 – 17
Direct Instruction:(15 minutes)
Yesterday we learned that when adding and subtracting integers, it’s important to remember “same signs add, different signs subtract”. Today we are going to take our knowledge of integer operations one step further and learn how to multiply and divide integers.
When we are multiplying integers, we are multiplying both the numbers and the signs. For example, -x time – y gives us –x-y. We remember from last week that same signs means add and different signs means subtract. So since we have two negatives, that really means that it is a positive.
If I multiply –x times y, I get – xy. Different signs, subtract, so I get –xy as my final answer.
We can also think about multiplication as repeated addition. If I have -4 x 2, it means I have -4 2 times, which is -4 + -4. If -4 + -4 = 8 then -4 x 2 = - 8
Students will write the following rule and examples in their notes:
Rule: When multiplying integers, two negatives become a positive product. A negative and a positive make a negative product.
Ex. – 5 x 3 Ex. -4 x -5 Ex. – 8 x 3
We can use what we know about fact families to help us with integer division. Dividing a negative and a positive gives us a negative. Dividing two negatives gives us a positive.
Have students write the following rule and examples in their notes:
Rule: A negative divided by a negative is a positive. A positive divided by a negative is a negative.
Ex. -18 ÷ -3 = 6 Ex. 24 ÷ -3 = -8
Ex. -12 ÷ 3 = -4Guided Practice: (5 minutes)
Complete the following problems as a class:
-3 x 6
12 ÷ -2
-12 x – 9
-72 ÷ -6
Assessment: (5 minutes)
Additional reinforcement of the skill can come from flashcards with multiplying and dividing integers.
Multiplying and dividing integers work-out