Decimals

1
Decimals

• What is a decimal

A piece of a whole (think about dollars and cents)
You can add, subtract, multiply and divide
decimals.
2
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.

3
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.

4
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
5
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)
6
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)
7
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?
8
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
9
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
10
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
11
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.

12
Assignment

• Measuring Up Pg.

13
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
14
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?

15
Dividing Decimals

• What is the question asking?

How many tickets were sold.
How do we find out how many tickets were sold?
16
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.
17
Decimals

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

18
Dividing DecimalsExample 2

• Arnold earned 29.75 in 3.5 hours. How much did
  he earn per hour?

19
Decimals

• What is the question asking?

How much did he earn per hour.
How do we find out how much he earned per hour?
20
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.
21
Decimals

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

22
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?

23
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.
24
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

25
Class Work

• Measuring Up Pg. 19 3-13 odd, 15-17

Advanced Glencoe Pg. 150-151 25-39, 49-51,
54, 55