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Decimals

- What is a decimal

A piece of a whole (think about dollars and cents)

You can add, subtract, multiply and divide

decimals.

Multiplying Decimals

- Multiplying decimals is just like multiplying

fractions!

- Model the value of your first decimal by shading

it in.

- Model the value of your second decimal by drawing

diagonal lines.

The Hundreds Grid

1

- The whole grid represents the whole number 1

- Each row or column represents one-tenth (0.1) of

the whole.

- Each individual unit represents one-hundredth

(0.01) of the whole.

Model 0.1 x 0.3

The product is determined by the number of units

that are overlapping with color (shaded and

striped)

Algorithm 0.1 0.3 0.03

x

Model 0.4 x 0.3

Algorithm 0.4 0.3 0.12

x

The product is determined by the number of units

that are overlapping with color (shaded and

striped)

Model 0.9 x 0.1

Algorithm 0.9 0.1 0.09

x

The product is determined by the number of units

that are overlapping with color (shaded and

striped)

DecimalsLets take a look!

- 0.1 0.4 0.9
- x 0.3 x 0.3 x 0.1
- 0.03 0.12 0.09

What's Happening?

Decimals

- Multiplying
- Dont worry about the decimal
- Align the numbers on the right
- Count the number of digits AFTER the decimal. In

the answer, move the decimal that many places - 0.74 x 3.2 0. 74
- x 3 . 2

3 digits after the decimal

2.368

Move the decimal 3 places

Shoot for the STARS!

- Kendra created a 5-day study schedule for her

exams. If the pattern continues, how many hours

will she study of the fifth day? - The table shows the number of hours she studies

in the first three days. - A) 3 B) 4 C) 4.5 D)3.75

Day 1 2 3

Hours 0.75 1.5 2.25

Kendra created a 5-day study schedule for her

exams. If the pattern continues, how many hours

will she study of the fifth day?

3/5 is between which two fractions?

Studied 1st day for 0.75 hrs 2nd day for 1.5

hrs 3rd day 2.25 hrs

I made a chart and noticed that she was

multiplying each day by 0.75. On the 5th day,

Kendra would study for 3.75 hours on the 5th day.

Day 1 2 3

Hours 0.75 1.5 2.25

1 x 0.75 0.75 2 x 0.75 1.50 3 x 0.75 2.25 4

x 0.75 3.00 5 x 0.75 3.75

Speed Test

- 1. Get a speed test, marker, and eraser.
- 2. Make sure your marker works!
- You have 1 minute to complete as many problems as

you can. - 4. Graph your results. Keep the graph in your

notebook. - 5. We will do this every day.

Assignment

- Measuring Up Pg.

Decimals

- Dividing
- There cannot be any decimals in the number

outside the house (divisor) - Move the decimals to make it a whole
- If you move the decimals in the divisor, move the

decimal in the dividend. - Push the decimal up
- 9.156 0.4

Move the decimal one place

22.89

Shoot for the STARS!Example 1

- A school took in a total of 1,773.75 during the

run of its spring musical. The cost per ticket

was 2.75. How many tickets were sold?

Dividing Decimals

- What is the question asking?

How many tickets were sold.

How do we find out how many tickets were sold?

Decimals

645

Move the decimals 2 places and push the decimal

up.

If the cost per ticket is 2.75 and the school

made 1,773.75, then there were 645 tickets sold.

Decimals

- Is our answer reasonable?
- Does the answer make sense?
- Does the answer COMPLETELY answer the question?

Dividing DecimalsExample 2

- Arnold earned 29.75 in 3.5 hours. How much did

he earn per hour?

Decimals

- What is the question asking?

How much did he earn per hour.

How do we find out how much he earned per hour?

Decimals

8.50

Move the decimals 1 place and push the decimal up.

Arnold worked 3.5 hours and made 29.75,

therefore, he earned 8.50 per hour.

Decimals

- Is our answer reasonable?
- Does the answer make sense?
- Does the answer COMPLETELY answer the question?

Shoot for the STARSExample 3

- Sarah drove a total of 101.6 miles. She got 25.4

miles per gallon. How many gallons of gas did

she use on her trip?

Decimals

4

Move the decimals 1 place and push the decimal up.

If she drove 101.6 miles, and she got 25.4 miles

per gallon, she used 4 gallons of gas.

What has to happen before we can divide?

- Ex 4 8.7 3
- Ex 5 5.8 4
- Ex 6 9.81 0.3
- Ex 7 0.0132 0.22

Class Work

- Measuring Up Pg. 19 3-13 odd, 15-17

Advanced Glencoe Pg. 150-151 25-39, 49-51,

54, 55