course 1 1-5 mental math 1-5 mental math course 1 warm up warm up lesson presentation lesson...
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Course 1
1-5 Mental Math1-5 Mental Math
Course 1
Warm UpWarm Up
Lesson PresentationLesson Presentation
Problem of the DayProblem of the Day
Course 1
1-5 Mental Math
Warm UpFind each sum or product.
1. 17 + 15
2. 29 + 39
3. 8(24)
4. 7(12)
5. 3(91)
6. 6(15)
32
68
192
84273
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
Course 1
1-5 Mental Math
Learn to use number properties to compute mentally.
Course 1
1-5 Mental Math
Vocabulary
Commutative PropertyAssociative PropertyDistributive Property
Course 1
1-5 Mental Math
Mental math means “doing math in your head.”
Many mental math strategies use number properties that you already know.
Course 1
1-5 Mental Math
COMMUTATIVE PROPERTY (Ordering)
Words Numbers
You can add or multiply numbers in any order.
18 + 9 = 9 + 1815 2 = 2 15
Course 1
1-5 Mental Math
ASSOCIATIVE PROPERTY (Grouping)
Words NumbersWhen 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
Evaluate 17 + 5 + 3 + 15.
17 + 5 + 3 + 15 Look for sums that are multiples of 10
40
Use the Commutative Property. 17 + 3 + 5 + 15
(17 + 3) + (5 + 15)
Use mental math to add.
20 + 20
Use the Associative Property to make groups of compatible numbers.
Course 1
1-5 Mental Math
Additional Example 1B: Using Properties to Add and Multiply Whole Numbers
Evaluate 4 13 5.
4 13 5
Look for products that are multiples of 10
260
Use the Commutative Property.13 4 5
13 (4 5)
Use mental math to multiply.13 20
Use the Associative Property to group compatible numbers.
Course 1
1-5 Mental Math
Check It Out: Example 1A
Evaluate 12 + 5 + 8 + 5.
12 + 5 + 8 + 5 Look for sums that are multiples of 10
30
Use the Commutative Property.12 + 8 + 5 + 5
(12 + 8) + (5 + 5)
Use mental math to add.
20 + 10
Use the Associative Property to make groups of compatible numbers.
Course 1
1-5 Mental Math
Check It Out: Example 1B
Evaluate 8 3 5.
8 3 5 Look for products that are multiples of 10
120
Use the Commutative Property.3 8 5
3 (8 5)
Use mental math to multiply.3 40
Use the Associative Property to group compatible numbers.
Course 1
1-5 Mental Math
DISTRIBUTIVE PROPERTY
Words NumbersWhen you multiply a number times a sum, you can• find the sum first and then multiply, or• multiply by each number in the sum and then add.
6 (10 + 4) = 6 14 = 846 (10 + 4) = (6 10) + (6 4) = 60 + 24 = 84
Course 1
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.
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.
Helpful Hint
Course 1
1-5 Mental Math
Additional Example 2A: Using the Distributive Property to Multiply
Use the Distributive Property to find the product.
6 35
6 35 = 6 (30 + 5) “Break apart” 35 into 30 + 5.
= 210
Use the Distributive Property.= (6 30) + (6 5)
Use mental math to add.
= 180 + 30 Use mental math to multiply.
Course 1
1-5 Mental Math Additional Example 2B: Using the Distributive
Property to Multiply
Use the Distributive Property to find the product.
9 87
9 87 = 9 (80 + 7) “Break apart” 87 into 80 + 7.
= 783
Use the Distributive Property.= (9 80) + (9 7)
Use mental math to add.
= 720 + 63 Use mental math to multiply.
Course 1
1-5 Mental Math
Check It Out: Example 2A
Use the Distributive Property to find the product.
4 27
4 27 = 4 (20 + 7) “Break apart” 27 into 20 + 7.
= 108
Use the Distributive Property.= (4 20) + (4 7)
Use mental math to add.
= 80 + 28 Use mental math to multiply.
Course 1
1-5 Mental Math
Check It Out: Example 2B
Use the Distributive Property to find the product.
6 43
6 43 = 6 (40 + 3) “Break apart” 43 into 40 + 3.
= 258
Use the Distributive Property.= (6 40) + (6 3)
Use mental math to add.
= 240 + 18 Use mental math to multiply.
Course 1
1-5 Mental Math
Lesson Quiz
Evaluate.
1. 18 + 24 + 2 + 6 2. 10 5 3
3. 13 + 42 + 7 + 8
Use the Distributive Property to find each
product.
4. 8 12 5. 6 15
6. 5 34 7. 3 71
15050
70
96 90
170 213