1. Decimals

2. Topics Covered Identifying place value Rounding Decimals
Adding and subtracting decimals
Multiplying and dividing decimals
Applications

3. Identifying Place Value

4. Examples
34.82
58.211

5. Rounding Decimal Numbers
Procedure for Rounding Decimals;
Underline the digit being rounded
Look to the digit to the right of the underlined digit
If the digit is 5 or greater, add 1 to the underlined digit
If the digit is less than 5, don’t change the underlined digit
Discard any digits to the right of the underlined digit
Examples:
Try these:
4.359 ; to the nearest hundredth
; to the nearest tenth
; to the nearest tenth
; to the nearest hundredth
; to the nearest thousandth

6. Adding & Subtracting Decimals
Line up the decimals vertically
Place the decimal points in line and the place-values will line up
“Square” the place values
Examples:
– 0.23

7. Multiplying Decimals
Ignore the decimals and multiply as if whole numbers
Count the number of place values in both decimals
Move the decimal in the answer the number of “place values”
Examples:
x ² 9.0 x

8. Dividing Decimals
Move the decimal in the dividend until it is a whole number
Move the decimal in the divisor the same number of places
Divide
Example: ÷

9. Application #1
A normal human red blood cell count is between 4.2 and 6.9 million cells per microliter. A cancer patient undergoing chemotherapy has a red blood cell count of 2.85 million cells per microliter. How far below the lower normal limit is this?

10. Application #2
A section of a bank statement is shown in the figure below. Find the mistake that was made by the bank.
date
action
debit
credit
balance $
1/2/10
Check #4214
$749.32
375.03
1/3/10
Check #4215
$37.29
337.74
1/4/10
Transfer from savings
$400.00
737.74
1/5/10
Paycheck $
1/6/10
Cash withdrawal
$150.00
688.95

11. Application #3
Water flows into a pool at a constant rate. The water level is recorded at several 1-hr intervals.
Time
Water Level
9:00AM
4.2 in.
10:00AM
5.9 in.
11:00AM
7.6 in.
12:00PM
9.3 in.
From the table, how many inches is the water level
rising each hour?
At this rate, what will the water level be at 1:00PM?
At this rate, what will the water level be at 3:00pm?

12. Application #4
A laptop computer was originally priced at $ and was discounted to $ By how much was it marked down?