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1-5 Mental Math
Warm Up
Problem of the Day
Lesson Presentation
Course 1
1-5 Mental Math
Warm Up
Find each sum or product.
1. 17 + 15
32
2. 29 + 39 68
3. 8(24)
192
4. 7(12)
5. 3(91)
84
273
6. 6(15)
90
Course 1
1-5 Mental Math
Problem of the Day
Determine the secret number from the
following clues:
• The number is a multiple of 5.
• It is divisible by 3.
• It is less than 200.
• Its tens digit equals the sum of its
other two digits.
165
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1-5 Mental Math
Learn to use number properties to
compute mentally.
Course 1
1-5 Mental
Insert Lesson
Math Title Here
Vocabulary
Commutative Property
Associative Property
Distributive Property
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1-5 Mental Math
Mental math means “doing math in
your head.”
Course 1
1-5 Mental Math
COMMUTATIVE PROPERTY (Ordering)
Words
You can add or
multiply numbers in
any order.
Course 1
Numbers
18 + 9 = 9 + 18
15  2 = 2  15
1-5 Mental Math
ASSOCIATIVE PROPERTY (Grouping)
Words
Numbers
When you are only
adding or only
multiplying, you
can group any of
the numbers
together.
(17 + 2) + 9 = 17 + (2 + 9)
(12  2)  4 = 12  (2  4)
Course 1
1-5 Mental Math
Additional Example 1A: Using Properties to
Add and Multiply Whole Numbers
A. Evaluate 17 + 5 + 3 + 15.
17 + 5 + 3 + 15
Look for sums that are
multiples of 10
17 + 3 + 5 + 15
Use the Commutative Property.
Use the Associative
(17 + 3) + (5 + 15) Property to make groups
of compatible numbers.
20 + 20
40
Course 1
Use mental math to add.
1-5 Mental Math
Additional Example 1B: Using Properties to
Add and Multiply Whole Numbers
B. Evaluate 4  13  5.
4  13  5
Look for products that are
multiples of 10
13  4  5
Use the Commutative Property.
13  (4  5)
Use the Associative Property to
group compatible numbers.
13  20
Use mental math to multiply.
260
Course 1
1-5 Mental Math
Try This: Example 1A
A. Evaluate 12 + 5 + 8 + 5.
12 + 5 + 8 + 5
Look for sums that are
multiples of 10
12 + 8 + 5 + 5
Use the Commutative Property.
(12 + 8) + (5 + 5)
Use the Associative Property to
make groups of compatible
numbers.
20 + 10
30
Course 1
Use mental math to add.
1-5 Mental Math
Try This: Example 1B
B. Evaluate 8  3  5.
835
Look for products that are
multiples of 10
385
Use the Commutative Property.
3  (8  5)
Use the Associative Property to
group compatible numbers.
3  40
Use mental math to multiply.
120
Course 1
1-5 Mental Math
DISTRIBUTIVE PROPERTY
Words
Numbers
When you multiply a
number times a sum, 6  (10 + 4) = 6  14
you can
= 84
• find the sum first
6  (10 + 4) = (6  10) + (6  4)
and then multiply, or
= 60
+
24
• multiply by each
=
84
number in the sum
and then add.
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1-5 Mental Math
When you multiply two numbers, you can
“break apart” one of the numbers into a sum
and then use the Distributive Property.
Helpful Hint
Break the greater factor into a sum that contains a
multiple of 10 and a one-digit number. You can add
and multiply these numbers mentally.
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1-5 Mental Math
Additional Example 2A: Using the Distributive
Property to Multiply
Use the Distributive Property to find the product.
A. Evaluate 6  35.
6  35 = 6  (30 + 5)
“Break apart” 35 into 30 + 5.
= (6  30) + (6  5)
Use the Distributive Property.
=
Use mental math to multiply.
=
Course 1
180
+
210
30
Use mental math to add.
1-5 Mental Math
Additional Example 2B: Using the Distributive
Property to Multiply
Use the Distributive Property to find the
product.
B. Evaluate 9 x 87.
9  87 = 9  (80 + 7)
“Break apart” 87 into 80 + 7.
= (9  80) + (9  7)
Use the Distributive Property.
=
Use mental math to multiply.
=
Course 1
720
+
783
63
Use mental math to add.
1-5 Mental Math
Try This: Example 2A
Use the Distributive Property to find the
product.
A. Evaluate 4 x 27.
4  27 = 4  (20 + 7)
“Break apart” 27 into 20 + 7.
= (4  20) + (4  7)
Use the Distributive Property.
=
Use mental math to multiply.
=
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80
+
108
28
Use mental math to add.
1-5 Mental Math
Try This: Example 2B
Use the Distributive Property to find the
product.
B. Evaluate 6  43.
6  43 = 6  (40 + 3)
“Break apart” 43 into 40 + 3.
= (6  40) + (6  3)
Use the Distributive Property.
=
Use mental math to multiply.
=
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240
+
258
18
Use mental math to add.
1-5 Mental
Insert Lesson
Math Title Here
Lesson Quiz
Evaluate.
1. 18 + 24 + 2 + 6 50
2. 10  5  3 150
3. 13 + 42 + 7 + 8 70
Use the Distributive Property to find each
product.
4. 8  12 96
5. 6  15
90
6. Angie wants to buy 3 new video games. How
much will she need to save if each game costs
$27? $81
Course 1