7th Grade Math

Lesson 3D Multiply and Divide Integers 111

ANIMALS One year, the estimated Australian koala population was

1,000,000. After 10 years, there were about 100,000 koalas. Find the

average change in the koala population per year.

_N - P

10

=

100,000 - 1,000,000

__

10

Nprevious population, 1,000,000. is the new population, 100,000. P is the

=

• 900,000
  _
  10
  or -90,000 Divide.

The koala population has changed by -90,000 per year.

h. WEATHER The average temperature in January for North Pole,

Alaska, is -24°C. Use the expression _^9 C +^160

5

to find this

temperature in degrees Fahrenheit. Round to the nearest

degree.

Operations with Integers

Operation Rule

Add

Same Signs: Add absolute values. The sum has the same

sign as the integers.

Different Signs: Subtract absolute values. The sum has

the sign of the integer with the greater absolute value.

Subtract To subtract an integer, add its opposite.

Multiply

and Divide

Same Signs: The product or quotient is positive.

Different Signs: The product or quotient is negative.

Real-World Link

An adult koala is

25–30 inches long

and weighs

15–30 pounds.

RR

A

Examples 1–3 Divide.

1. 32 ÷ (-8) 2. - 16 ÷ 2 3. _^42
   
   
   • 7
   
   
   
   


2. 
   
   
   
   • 30 ÷ (-5) 5. 55 ÷ 11 6. _-^16
     -4
   
   
   
   

Example 4 ALGEBRA Evaluate each expression if x^ = 8 and y^ =^ - 5.

77 15 ÷ y 8. xy ÷ (-10)

Example 5 9. TEMPERATURE The lowest recorded temperature in Wisconsin is -55°F

on February 4, 1996. Use the expression

5(F - 32)

_

9

to find this temperature

in degrees Celsius. Round to the nearest tenth.

102_113_C2L3_895130.indd 111 12/29/09 12:51 PM