today we will multiply using decimals. multiply = multiply means to add all equal groups together a...
TRANSCRIPT
Today we will multiply using decimals.
multiply = Multiply means to add all equal groups together a set number of
timesDecimals=numbers less than zero
Remember the 100’s chart? When you multiply two numbers that are decimals, you get the product!
Here is a model of the product of 0.7 and 0.3.1
1
0.3
0.7
Because 21 of the 100 squares are shaded, 0.7 0.3
Multiplying Decimals
= 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?
3.2 1x 4
4 8 1 2 .
1St step:Ignore
the decimal
point and
just multiply!!
2St step:Count the
number
of digits
that follow
the decimal.
12
12
Pg. 1 Pg. 23rd step:Place the
decimal.
Check by
using estimation.
Let’s try one together!
5.82
0.41
2 decimal places
2 decimal places
5 8 22 3 2 8
4 decimal places
–––+––––––
2.3 8 6 2–––––––
1234
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
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
0.41 0.4
Round to the nearest whole number.
Round to the nearest tenth.
Because 6 0.4 = 2.4, the product of the previous example is reasonable.
6.45
18
2 decimal places
0 decimal places
5160645
––––––116.10
Because 6 20 = 120, the product is reasonable.
Multiplying Decimals
–––+––––––
After you place the decimal point, you can drop any zeros at the end of an answer.
2 decimal places
CHECK
ANSWER 6.45 18 = 116.1
1. Ignore the decimal and just multiply
2. Count the number of digits that follow the decimal
3. Place the decimal
1.273
0.06
3 decimal places
2 decimal places
76380.0 5 decimal places
Because 1 0.06 = 0.06, the product is reasonable.
––––––– –––+
CHECK
ANSWER 1.273 0.06 = 0.07638
1. Ignore the decimal and just multiply
2. Count the number of digits that follow the decimal
3. Place the decimal
1. Ignore the decimal and just multiply
2. Count the number of digits that follow the decimal
3. Place the decimal
9.7 6 x 5.9
9.7 6 x 5.9
9.7 6 x 5.9
9.76
5.9
8 7 8 44 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
5 7 69 6 0
––––––
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 add all equal groups
together a set number of times
What does multiply mean?
What are decimals?
Decimals=numbers less than zero