NOTES Multiplying Decimals

MULTIPLYING DECIMALS:1st MULTIPLY AS NORMAL2nd Count the number of digits behind the decimal in the factors (in the problem)

3rd That is how many numbers should be behind the decimal in your answer

Name: ___________ Date: __________Math ___ hr MC2 pg 65 section 2.3

EXAMPLE 1 Multiplying Decimals

582

2 3 8 6 2

5.82

0.41

23280

2 decimal places

+ 2 decimal places

4 decimal places.

EXAMPLE 2

a. 6.45

5160

1 1 6 1 0

182 decimal places

2 decimal places ANSWER

6.45 18 = 116.1

6450

+ 0 decimal places

Multiplying Decimals

.

EXAMPLE 2

b. 1.2730.06

3 decimal places

5 decimal places

ANSWER

1.273 0.06 = 0.07638

+ 2 decimal places

7638

Multiplying Decimals

0.07638

EXAMPLE 2GUIDED PRACTICE for Examples 1 and 2

I am giving you the digits that are in your answer. PLACE THE DECIMAL.

1. 1.4 7.2 = 1 0 0 8

10.08ANSWER

2. 0.98 * 0.21 = 2 0 5 8

0.2058ANSWER

3. 2.351 * 1.6 = 3 7 6 1 63.7616ANSWER

EXAMPLE 3 Finding AreaFinding Area with Decimals

Central Park

Central Park, in New York City, is a rectangular park about 2.5 miles long and about 0.5 mile wide. What is the area of Central Park?

SOLUTIONA = l * w

= 2.5 * 0.5= 1.25

Write formulaWrite formula for area of a rectangle.

SubstituteSubstitute 2.5 for l and 0.5 for w.

Solve!Solve! Multiply.

The area of Central Park is about 1.25 square miles.

ANSWER

L= 2.5 mi

W= 0.5 mi

EXAMPLE 3GUIDED PRACTICE for Example 3

Find the area of the rectangle.7.

ANSWER 18.84 in.2

8.

ANSWER 36.12 cm2

A = L * WA = 9.42 * 2

A = L * WA = 8.4 * 4.3

A = 3 6 1 2

A = 1 8 8 4

EXAMPLE 3GUIDED PRACTICEEXAMPLE 4 Standardized Test Practice

STEP 1Calculate the least possible cost by using $.25 as the price for all of the fruits and vegetables.

C = 14.4 0.25 = $3.60

SOLUTION

EXAMPLE 3GUIDED PRACTICEEXAMPLE 4

STEP 2

Calculate the greatest possible cost by using $2.10 as the price for all of the fruits and vegetables.

C = 14.4 2.10 = $30.24ANSWER

The least cost for food is $3.60 and the greatest cost is $30.24. The correct answer is C. A B C D

Standardized Test Practice

EXAMPLE 3GUIDED PRACTICEEXAMPLE 3GUIDED PRACTICE for Example 4

ANSWER $4.20 to $35.28

In Example 4, suppose you buy 16.8 pounds of fruits and vegetables. What is the range of the amount you might spend?

What If?9.

EXAMPLE 2GUIDED PRACTICE

4. 2.6 m

Evaluate the expression when m = 3.26 and n = 1.24.

8.476ANSWER

5. 1.7 n

2.108ANSWER

6. mn

4.0424ANSWER

for Examples 1 and 2

MULTIPLYING DECIMALS:

1st MULTIPLY AS NORMAL2nd Count the number of digits behind the decimal in the factors (numbers in the problem)

3rd That is how many numbers should be behind the decimal in your answer

Name: ___________ Date: __________Math ___ hr MC2 pg 65 (2-7all, 9-20 evens,

25-28 all, 29-34 evens)