Download Strategies For Multiplying Decimals by Whole Numbers

5 Minute Math Review
1. Solve 2.478 + 3.01=
2. Solve 10.47 - 2.221=
3. What is 98.47 rounded to the nearest ones?
4. Solve & show your work 315 x 26=
5. What is 81.94 rounded to the nearest tenth?
Multiplying Decimals
Ob
jective: Today we will learn strategies to multiply decimals by
whole numbers, multiply decimals by decimals and use a representation to
show our work.
Vocabulary:
- Multiplication: repeated addition.
-Ex. 5 x 3 = 5 + 5 + 5 = 15
Strategies For Multiplying Decimals by Whole Numbers:
(
Write down this strategy in your notebook)
Strategy
# 1. Using 10 x 10 Grid:
Example Problem: 0.21 x 3
1. Take your decimal number (your first factor) and shade in that many squares of your hundreds block.
2. Do this as many times as the second factor (your whole number)
3. Count up your boxes and that’s how many hundredths you have.
4. Write in proper decimal form.
.21 x 3= .63
.21
.21
.21
Strategies For Multiplying Decimals by Whole Numbers:
(
Write down this strategy in your notebook)
Strategy
# 2. Standard Multiplication Algorithm
Example Problem: 0.21 x 3
Step 1: Multiply as you would with whole numbers (Pretend the decimals aren't there).
Step 2: Count how many digits you have after EVERY decimal point in the problem.
Step 3: Move the decimal point to the LEFT as many places as there are digits behind the decimal.
Step 1:
63
Step 3:
.21
x 3
63
.21
x
Step 2:
<-- 2 places
3
.21
x
63.
3
Final Answer:
.21
x 3
.63
Strategies For Multiplying Decimals by Whole Numbers:
(Write down this strategy in your notebook)
Strategy
# 3. Repeated Addition
Example Problem: 0.21 x 3
0.21
0.21
+ 0.21
0.63
Practice: (Do in your notebook)
Use whatever strategy that works best for you, unless asked to use a specific strategy.
1. Solve .64 x 4=
2. Solve .37 x 8=
3. Solve 0.5 x 45=
Stop here and we will continue the rest of the notes tomorrow. Rest of the class
period will be in the computer lab. Please make sure you take a pencil to the
computer lab and you clean up and push in your chairs when you leave.
5 Minute Math Review
1. Solve 248 x 0.6=
2. Solve
.37 x 12=
3. Solve .45 x 9=
214 x 0.4=
4. Solve
Multiplying Decimals
(continued)
jective: Today we will learn strategies to multiply decimals by whole
numbers, multiply decimals by decimals and use a representation to show
our work.
Ob
Strategies For Multiplying Decimals by Decimals:
(
Write down this strategy in your notebook)
Strategy
# 1. Using 10 x 10 Grid:
Example Problem: 0.4 x 0.6=
1. Take your first decimal number
(your first factor) and shade in that many squares of your
hundreds block vertically (up and down).
2. Take your second decimal number (your second
factor) and shade in that many squares of your hundreds
block in the opposite direction (side to side).
3. Count up the boxes that are overlapped by both
shadings.
4. Write in proper decimal form.
Strategies For Multiplying Decimals by Decimals:
(
Write down this strategy in your notebook)
Strategy
# 2. Standard Multiplication Algorithm:
Example Problem: 0.4 x 0.6=
Step 1: Multiply as you would with whole numbers.
Step 2: Count how many digits you have after EVERY decimal point in the problem.
Step 3: Move the decimal point to the LEFT as many places as there are digits behind the decimal.
Step 1:
.4 <--- 1 place
x .6 <--- 1 place
24
2
.4
x .6
24
Step 3:
Step 2:
.4
x .6
places
total
24.
Final Answer:
.4
x .6
.24
Practice: (Do in your notebook)
Use whatever strategy that works best for you, unless asked to use a specific strategy.
1. Solve 1.64 x 4=
2. Solve .7 x .8=
3. Solve 0.5 x 0.12=
4. Solve .48 x .25=
*When finished with practice:
- Do flower power activity.
-Start working on your small group packet.
68, 69, 70, 71)
-If you need help, raise your hand.
(p.67,