Decimals

Decimals and the Calculator
When a number containing a
decimal is entered into a calculator,
use the decimal key • . 53.8
would be entered as 53 • 8.
TIP
STOP AND CHECK
86 CHAPTER 3
EXAMPLE 1 Subtract 26.3 - 15.84.
2 6 5
.3
12
0
10
- 1 5.8 4
1 0.4 6
2 Multiply decimals.
Write the numbers so that the digits align according to their place values.
Subtract the numbers, regrouping as you would in whole-number subtraction.
The difference of 26.3 and 15.84 is 10.46.
1. Add: 67 + 4.38 + 0.291 2. Add: 57.5 + 13.4 + 5.238
3. Subtract: 17.53 - 12.17
5. Garza Humada purchased a shirt for $18.97 and paid with a
$20 bill. What was his change?
4. Subtract: 542.83 - 219.593
6. The stock of FedEx Corporation had a high for the day of
$120.01 and a low of $95.79, closing at $117.58. By how
much did the stock price change during the day?
Suppose you want to calculate the amount of tip to add to a restaurant bill. A typical tip in the
United States is 20 cents per dollar, which is 0.20 or 0.2 per dollar. To calculate the tip on a bill
of $28.73 we multiply 28.73 * 0.2.
We multiply decimals as though they are whole numbers. Then we place the decimal point
according to the quantity of digits in the decimal parts of the factors.
HOW TO
Multiply decimals
1. Multiply the decimal numbers as though they are whole
numbers.
2. Count the digits in the decimal parts of both decimal
numbers.
3. Place the decimal point in the product so that there are
as many digits in its decimal part as there are digits you
counted in step 2. If necessary, attach zeros on the left
end of the product so that you can place the decimal
point accurately.
EXAMPLE 2 Multiply
2.35
* 0.015
1175
235
0.03525
two decimal places
three decimal places
five decimal places.
The product of 2.35 and 0.015 is 0.03525.
2.35 * 0.015.
Multiply 3.5 * 0.3
3.5 one place
* 0.3 one place
1.0 5 two places
One 0 is attached on the left to accurately place the
decimal point.