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2.2 Problem Solving With Rational Numbers in Decimal Form (Page 55 – 62)
Example 1: Add and Subtract Rational Numbers in Decimal Form.
A.
2.65 + (-3.81)
Estimate
3 + -4 = - 1
Determine the
difference
3.81
 2.65
B.
Estimate
Change signs
Determine the
difference
1.16
Since 3.81  2.65 the answer is – 1.16
-5.96 – (-6.83)
-6 – (-7)
-6 +7 = 1
6.83
 5.96
0.87
Since 6.83  5.96 the answer is 0.87
Example 2: Multiply and Divide Rational Numbers in Decimal Form
A.
0.45 × (-1.2)
Estimate
0.5 × (- 1) = -0.5
Method 1: Paper and Pencil
Determine the
1.2

0
.45
product
60
 480
Determine the
sign of the
product
MA 09 – Chapter 2
B.
-2.3 ÷ (-0.25)
Estimate
-2 ÷ -0.2 = 10
Method 2: Calculators
Determine the
-2.3 ÷ (-0.25) = 9.2
quotient
0.540
-0.54
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Example 3: Apply Operations With Rational Numbers in Decimal Form
On Saturday, the temperature at the Blood Reserve near Stand Off,
Alberta decreased by 1.2 °C/h for 3.5 h. It then decreased by
0.9°C/h for 1.5 h.
a) What was the total decrease in temperature?
Method 1: Calculate in Stages
You can represent the temperature
decrease in the temperatures.
Method 2: Evaluate One Expression
The total temperature decrease can be
represented by
3.5 × (-1.2) =-4.2
3.5 × (-1.2) + 1.5 × (0.9) = -1.35
1.5 × (-0.9) = -1.35
- 4.2 + (- 1.35) = -5.55
Add to determine the total temperature
decrease.
The total decrease in temperature is
- 5.55°C.
- 4.2 + (- 1.35) = -5.55
The total decrease in temperature is
- 5.55°C.
b) What was the average rate of decrease in temperature?
How many hours in total?
 5.55
 1.11
5
3.5 + 1.5 = 5.0 hours
The average rate of decrease in temperature was 1.11°C/h.
Practice Problems – Page 60 Qs – 5, 7, 9, 10, 12, 13, 15, 16, 22, 23
MA 09 – Chapter 2
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