Transcript EDI NS 2_1 Multiplying Decimals

Today we will multiply
using decimals.
multiply = Multiply means to add all
equal groups together a set number of
times
Decimals=numbers less than zero
Multiplying Decimals
Remember the 100’s chart? When you multiply
two numbers that are decimals, you get the
product!
0.7
0.3
1
Here is a model of the product of 0.7 and 0.3.
1
Because 21 of the 100 squares are
shaded, 0.7  0.3 = 0.21.
APK
You go to the store to buy an iPod. The
price is $199.00 for an iPod Touch. Do you
pay $199.00 or do you pay 217.41?
You pay 217.41 because of sales
tax and you must multiply by
.0925% to calculate the tax.
Multiply
• Multiply means to add all equal groups
together a set number of times
• Example: 4 x 3=12
=
12
Decimal
• A decimal is a number less than 1.
For example
• $0.70
• 10.50989
• $25.50
Importance
–When you purchase something in the
store, you always need to know how
much it will cost with sales tax.
–It will help you on any tests!
–What would be other reasons to know
how to multiply with decimals?
Let’s try one together!
121
3.2
x
4
1 2 8 4.
2
1
Pg. 2
Let’s try some more!
1. Ignore the
decimal and
just multiply
2. Count the
number of
digits that
follow the
decimal
3. Place the
decimal
5.82
 0.41
––––––
582
2 328
–––––––
2.3 8 6 2
1234
2 decimal places
2 decimal places
+
–––
4 decimal places
Checking Reasonableness To check that the product in the example is
reasonable, round each factor to the place value of the leading digit, then
multiply. The leading digit of a number is the first nonzero digit.
5.82
6
Round to the nearest whole number.
0.41
0.4
Round to the nearest tenth.
Because 6  0.4 = 2.4, the product of the previous example is reasonable.
1. Ignore the
decimal and
just multiply
2. Count the
number of
digits that
follow the
decimal
3. Place the
decimal
Multiplying Decimals
6.45
 18
––––––
5160
645
––––––
116.10
2 decimal places
+ 0 decimal places
–––
2 decimal places
After you place the decimal
point, you can drop any zeros
at the end of an answer.
ANSWER 6.45  18 = 116.1
CHECK
Because 6  20 = 120, the
product is reasonable.
1.273
1. Ignore the
decimal and
just multiply
2. Count the
number of
digits that
follow the
decimal
3. Place the
decimal
0.06

–––––––
0.07638
3 decimal places
+ 2 decimal places
–––
5 decimal places
ANSWER 1.273  0.06 = 0.07638
CHECK
Because 1  0.06 = 0.06,
the product is reasonable.
9.7 6
x 5.9
1. Ignore the
decimal and
just multiply
2. Count the
number of
digits that
follow the
decimal
3. Place the
decimal
9.76
 5.9
––––––
8784
4 8 80
–––––––
57. 5 8 4
123
1. Ignore the
decimal and
just multiply
2. Count the
number of
digits that
follow the
decimal
3. Place the
decimal
1.92
 5.3
––––––
576
960
–––––––
10. 1 7 6
123
1. Ignore the
decimal and
just multiply
2. Count the
number of
digits that
follow the
decimal
3. Place the
decimal
Let’s review what we
learned!
multiply = Multiply means to
What does
add all equal groups
multiply mean?
What are
decimals?
together a set number of
times
Decimals=numbers
less than zero