### 9-23 PPT

```5 Minute Check
Estimate each product.
1. 9.7 x 3
2. 3.4 x 5
3. 17.5 x 8
Multiply.
4. 1.5 x 6
5. 3.1 x 13
6.
3.48 x 25
5 Minute Check
Estimate each product.
1. 9.7 x 3
5 Minute Check
Estimate each product.
1. 9.7 x 3
10 x 3 = 30
5 Minute Check
Estimate each product.
2. 3.4 x 5
5 Minute Check
Estimate each product.
2. 3.4 x 5
3 x 5 = 15
5 Minute Check
Estimate each product.
3. 17.5 x 8
5 Minute Check
Estimate each product.
3. 17.5 x 8
18 x 8 = 144
5 Minute Check
Multiply.
4. 1.5 x 6
5 Minute Check
Multiply.
4. 1.5 x 6
1.5
x 6
9.0
1 decimal place
1 decimal place
5 Minute Check
Multiply.
5. 3.1 x 13
5 Minute Check
Multiply.
5. 3.1 x 13
3.1
x 13
93
+ 310
40.3
1 decimal place
1 decimal place
Don’t forget the zero
5 Minute Check
Multiply.
6. 3.48 x 25
5 Minute Check
Multiply.
6. 3.48 x 25
3.48 2 decimal places
x 25
1740
+ 6960
87.00 2 decimal places
Don’t forget the zero
Flashcards!
Wednesday, Oct 9
Lesson 3.2 and 3.4
Multiplying Decimals by Decimals
Multiplying Decimals by Decimals
Objective: To understand how to estimate
and multiply decimals by decimals.
Multiplying Decimals by Decimals
At the end of this lesson you should be able to
How do you determine which place value to use when
multiplying decimals by decimals?
Why is estimating not as helpful when multiplying very
small numbers?
Multiplying Decimals by Decimals
To multiply decimals, multiply as normal and
then place the decimal point.
Multiplying Decimals by Decimals
Find the product of 8.7 and 2.8.
First round the numbers to the nearest whole
number to get an estimate.
What does 8.7 round to?
Digits from 0 to 4 round down and digits from
5-9 round up.
Multiplying Decimals by Decimals
Find the product of 8.7 and 2.8.
First round the numbers to the nearest whole
number to get an estimate.
What does 8.7 round to? 9
What does 2.8 round to?
Multiplying Decimals by Decimals
Find the product of 8.7 and 2.8.
First round the numbers to the nearest whole
number to get an estimate.
What does 8.7 round to? 9
What does 2.8 round to? 3
Multiplying Decimals by Decimals
Find the product of 8.7 and 2.8.
First round the numbers to the nearest whole
number to get an estimate.
9 x 3 = 27, so
8.7 x 2.8 ≈ 27
Multiplying Decimals by Decimals
Find the product of 8.7 and 2.8.
To multiply decimals.
Step 1 – Stack the numbers with the number
with the most digits on top.
8.7
x 2.8
(Since both numbers have 2 digits, either could be
on top)
Multiplying Decimals by Decimals
Find the product of 8.7 and 2.8.
To multiply decimals.
Step 2 – Multiply the digits.
8.7
x 2.8
696
+1740
2436
Don’t forget to add the zero.
Multiplying Decimals by Decimals
Find the product of 8.7 and 2.8.
To multiply decimals.
Step 3 – Determine the number of decimal
places in the factors to locate the decimal
place in the product.
8.7
1 decimal place
x 2.8
+ 1 decimal place
696
+1740
24.36
2 decimal places
Multiplying Decimals by Decimals
Find the product of 8.7 and 2.8.
8.7
x 2.8
696
+1740
24.36
Multiplying Decimals by Decimals
Find the product of 8.7 and 2.8.
24.35 ≈ 27
Multiplying Decimals by Decimals
Find the product of .98 and 7.3
Estimate?
Multiplying Decimals by Decimals
Find the product of .98 and 7.3
Estimate?
1 x 7 = 7, so
.98 x 7.3 ≈ 7
Next?
Multiplying Decimals by Decimals
Find the product of .98 and 7.3
.98
x 7.3
Next?
Multiplying Decimals by Decimals
Find the product of .98 and 7.3
.98
x 7.3
294
+6860
7154
Next?
Don’t forget to add a zero
Multiplying Decimals by Decimals
Find the product of .98 and 7.3
.98
x 7.3
294
+6860
7.154
2 decimal places
+1 decimal place
3 decimal places
Multiplying Decimals by Decimals
Find the product of .98 and 7.3
.98
x 7.3
294
+6860
7.154
2 decimal places
+1 decimal place
3 decimal places
7.154 ≈ 7
Multiplying Decimals by Decimals
Find the product of 3.6 and 0.05.
Estimate?
Multiplying Decimals by Decimals
Find the product of 3.6 and 0.05.
4 x 0 = 0, so
3.6 x 0.05 ≈ 0
Multiplying Decimals by Decimals
Find the product of 3.6 and 0.05.
4 x 0 = 4, so
3.6 x 0.05 ≈ 0
Actual product?
Multiplying Decimals by Decimals
Find the product of 3.6 and 0.05
0.05
x 3.6
0030
+ 0015
0.045
2 decimal places
+1 decimal place
3 decimal places
Multiplying Decimals by Decimals
Find the product of 3.6 and 0.05
0.05
x 3.6
030
+0150
0.180
2 decimal places
+1 decimal place
3 decimal places
0.180 ≈ 0
Multiplying Decimals by Decimals
Find the product of 0.112 and 7.2
Estimate?
Multiplying Decimals by Decimals
Find the product of 0.112 and 7.2
Estimate?
0 x 7 = 0, so
0.112 x 7.2 ≈ 0
Actual product?
Multiplying Decimals by Decimals
Find the product of 0.112 and 7.2
0.112
x 7.2
0224
+07840
.8064
3 decimal places
+1 decimal place
4 decimal places
Multiplying Decimals by Decimals
Find the product of 0.112 and 7.2
0.112
x 7.2
0224
+07840
.8064
3 decimal places
+1 decimal place
4 decimal places
0.8064 ≈ 0
Multiplying Decimals by Decimals
Find the product of 1.4 and 0.067
Estimate?
Multiplying Decimals by Decimals
Find the product of 1.4 and 0.067
Estimate?
1x0=0
1.4 x 0.067 ≈ 0
Actual product?
Multiplying Decimals by Decimals
Find the product of 1.4 and 0.067
0.067
x 1.4
0268
+00670
0.0938
3 decimal places
+1 decimal place
4 decimal places
Multiplying Decimals by Decimals
Find the product of 1.4 and 0.067
0.067
x 1.4
0268
+00670
0.0938
3 decimal places
+1 decimal place
4 decimal places
0.0938 ≈ 0
Multiplying Decimals by Decimals
Mr. Avery’s car can travel 28.45 miles on one gallon of gas.
If his gas tank holds 11.5 gallons, how far can he travel on
one tank?
Estimate?
Multiplying Decimals by Decimals
Mr. Avery’s car can travel 28.45 miles on one gallon of gas.
If his gas tank holds 11.5 gallons, how far can he travel on
one tank?
Estimate?
28 x 12 = 336
Keep in mind
28 x 12 = 28 x 10 + 28 x 2
= 280 + 56 = 336
Actual product?
Multiplying Decimals by Decimals
Mr. Avery’s car can travel 28.45 miles on one gallon of gas.
If his gas tank holds 11.5 gallons, how far can he travel on
one tank?
28.45
x 11.5
14225
28450
+284500
327.175
2 decimal places
+1 decimal place
3 decimal places
Multiplying Decimals by Decimals
Mr. Avery’s car can travel 28.45 miles on one gallon of gas.
If his gas tank holds 11.5 gallons, how far can he travel on
one tank?
28.45
x 11.5
14225
28450
+284500
327.175
2 decimal places
+1 decimal place
3 decimal places
Is this a reasonable answer? 327.175 ≈ 336
Multiplying Decimals by Decimals
Determine whether the following statement is
always, sometimes or never true.
The product of two decimals less than 1 is less
than either of the factors.
Multiplying Decimals by Decimals
Determine whether the following statement is
always, sometimes or never true.
The product of two decimals less than 1 is less
than either of the factors.
Always.
0.3 x 0.5 = .15, which is less than 0.3 and 0.5
0.75 x 0.6 = 0.45
Multiplying Decimals by Decimals
Complete the Mid-Chapter Check on page
214. When complete bring to the desk and
show Mr. Avery.
Agenda Notes
Homework –Homework Practice 3-2/3-4
Due Thursday, Oct 10
Mid-Chapter 3 Quiz –Thursday, Oct 10
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