Transcript Reusable Learning Object

Reusable Learning Object
Multiplying 2-digit
Numbers
Maggie Martinez
Summer 2005
Overview
Multiplication is used everyday in
life. By using two-digit
multiplication, we can find the
product of an equation a lot
faster than counting each
individual piece. Learning how to
multiply is critical in doing higher
math such as division, fractions
and algebra.
Overview – Introduction and Importnace
After completing this lesson, you will be
able to correctly multiply two factors
when one of the factors has 2-digits.
Prerequisites
Before proceeding with this lesson, you should have a
basic understanding of the following math concepts:
• Place value
• Addition
• Number sentences
Overview – Objectives and Prerequisites
Today is your lucky day!
Ms. Martinez is going to order
pizza for the whole class!
Before she can do so, she needs
YOU to find out how many slices
of pizza the students will eat.
There are 23 students in the class.
If each student eats 2 slices, how
many slices does Ms. Martinez
have to order?
Overview – Scenario
Outline
What are the parts of a place value chart?
What are the different symbols that can be used
in a number sentence?
What is a factor?
What is a product?
In what way are addition and multiplication
related?
How to multiply by 2-digits
Overview - Outline
An equation is a
mathematical number
sentence where the left
side of the equal sign has
the same value as the
right side.
Equation
Symbols
There are so many
different symbols
in a math equation.
What are they?
Type of
equation
Example of the
symbol in an
equation
+
Addition
2+3=5
-
Subtraction
3–2=1
Multiplication
2x3=6
2*3=6
/
Division
6/3=2
=
Equal
2+3=5
X or *
Concept RIO – Symbols in a Number Sentence
All multiplication number sentences contain factors and
products. You will need to identify the parts of a
multiplication number sentence
8
Factor
x
8
Factor
A factor is a whole number
that multiplies with another
number
=
64
Product
A product is the
answer to a
multiplication
equation; it is
the result of
multiplying two
numbers
Concept RIO - Factors and Products
EXAMPLE
Multiplication
symbol
2
x 3
6
Factors
Product
Concept RIO – Factors and Products
NON-EXAMPLES
2
+
Addend
2
=
Addend
4
Sum
These are not examples of the use of factors and
products.
Notice that the number sentences do not use a
multiplication symbol.
12
Dividend
/
3
Divisor
=
4
Quotient
Concept RIO – Factors and Products
Equation, Symbols, Factors, and Products Practice Exercises
For each equation, determine whether number sentence is correctly identified.
Example
CORRECT or INCORRECT
This number sentence is correct
because the 8 is a factor in the
multiplication
8
x
8
=
64
+
2
=
10
=
15
Factor
PRACTICE EXERCISES
1. CORRECT or INCORRECT
This number sentence is not
correct because the 2 is an
addend. This is an addition
equation.
2. CORRECT
or
8
Factor
INCORRECT
This number sentence is correct
because the 15 is a product; it
is an answer in the
multiplication equation.
5
x
3
Product
Concept Practice
Factors and Products
PLACE VALUE CHART
Each digit has a value depending on its place in a number.
The place value chart helps us to understand the value of
each number. In order to complete a multiplication problem,
you will need to know the place value of each digit.
Thousands
Hundreds
Tens
Ones
1,000
100
10
1
,
Fact RIO - Place Value Chart
The number 235
can be put into
the chart, then I
can figure out
how much each
digit is worth.
Thousands
Hundreds
Tens
Ones
1,000
100
10
1
,
2
3 5
Notice that the value increases
as we move to the left
Fact RIO - Place Value Chart
PRACTICE EXERCISE A
Drag and drop the name and place value block in the correct column.
Ones
_______
_________
________
_______
Hundreds
Tens
Thousands
PRACTICE EXERCISE B
Given the following numbers, click on the the correct place value that
names the underlined digit.
8,156
Ones
Tens
Hundreds
Thousands
3,298
Ones
Tens
Hundreds
Thousands
4,672
Ones
Tens
Hundreds
Thousands
Fact Practice
Place Value Chart
Multiplication is just a very quick way of adding
numbers together.
2+2+2+2+2+2 = 12
How many
twos are in
the
problem?
6
So a quicker
way of saying
2+2+2+2+2+2
is 2 X 6
Multiplication and addition are very closely related. You
can change a long addition number sentence into a very
short multiplication number sentence.
Process RIO – Addition and Multiplication
Directions: Decide whether you can use a multiplication number
sentence as a faster way to solve the problem. If so, then solve
the problem. If not, provide a reason.
You are opening up a dog walking business. Every day of the week, you are to walk 3 dogs. How
many dogs will you have walked at the end of the week?
Sunday
Click for answer
Monday
Tuesday
Wednesday
Thursday
Friday
Saturday
You CAN solve this problem with multiplication!
3 dogs X 7 days in the week
3 X 7 = 21
Process Practice
Addition and Multiplication
Now that you can correctly identify the parts of a
multiplication number sentence, we can learn how to multiply
when one of the factors has 2-digits. There are 4 steps.
We’ll be using this multiplication problem
34
x2
Procedure RIO - How to Multiply by 2-digits (without regrouping)
Step
Action
1
Begin by multiplying
the digits in the ones
place value
2
Put the product in
the ones place
3
Multiply the bottom
factor by the top
factor that is in the
tens place
4
Place the product in
the tens place value
column
Example
T
O
3 4
x 2
T
O
T
O
T
O
3 4
x 2
8
3 4
x 2
8
3 4
x 2
6 8
Procedure RIO – How to Multiply by 2-digits
You have decided that now you can start to solve the pizza
problem that will allow Ms. Martinez to order for the whole
class. In order to do so, you have to multiply 23 X 2.
Number the steps to solving the equation correctly.
Multiply the digits in the ones place value
Place the product in the tens place value column
Put the product in the ones place
Multiply the bottom factor by the top factor that is in the tens place
1
2
3
4
Procedure Practice
How to Multiply by 2-digits
Review
This completes the lesson on how to multiply with a 2-digit
factor. You should be able to label the parts of a place value
chart, identify symbols, factors and products in a number
sentence, and be able to solve a 2-digit multiplication equation.
You should now be able to
tell Ms. Martinez how
many slices of pizza to
order for the class by
solving 23 x 2.
T O
2 3
X2
4 6
Ms. Martinez should
order 46 slices!
Summary
Next Steps
It is recommended that you research the items listed below to gain a
fuller understanding of this subject.
• Place value
• Expanded Form of a number
• Multiplying using partial-product
Additional Resources
The following item will provide more information on the topics that
were covered in this lesson.
• A Math Dictionary for Kids, Jenny Eather. An animated
interactive dictionary for kids.
http://www.teachers.ash.org.au/jeather/indexmdfk.html
Quiz
Exercise A
CORRECT or
INCORRECT
This number sentence is NOT
correct because the 4 is the
difference; it is an answer in a
subtraction equation.
7
-
3
=
4
Product
Exercise B
For each number drag and drop blocks to make a visual representation using place
value blocks. Use as many blocks of each as needed.
Number
3,298
4,672
Visual
Quiz
Exercise C
Solve the following problems. If necessary, refer to the action table to the right.
Step
Action
1
Begin by multiplying the digits in the ones
place value
2
Put the product in the ones place
3
Multiply the bottom factor by the top factor
that is in the tens place
4
Place the product in the tens place value
column
T O
92
x1
T O
34
x2
T O
43
x2
Reusable Learning Object
Multiplying 2-digit Numbers
Maggie Martinez
Summer 2005