Multiplying 2-digit Numbers

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• Multiplying 2-digit Numbers
• Maggie Martinez
• Summer 2005

Reusable Learning Object
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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
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Overview Objectives and Prerequisites
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

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Overview Scenario
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?
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Overview - Outline
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
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Concept RIO Symbols in a Number Sentence
An equation is a mathematical number sentence
where the left side of the equal sign has the
same value as the right side.
There are so many different symbols in a math
equation. What are they?
Equation Symbols Type of equation Example of the symbol in an equation
Addition 2 3 5
- Subtraction 3 2 1
X or Multiplication 2 x 3 6 2 3 6
/ Division 6 / 3 2
Equal 2 3 5
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Concept RIO - Factors and Products
All multiplication number sentences contain
factors and products. You will need to identify
the parts of a multiplication number sentence
8 Factor
64 Product
8 Factor
x

A product is the answer to a multiplication
equation it is the result of multiplying two
numbers
A factor is a whole number that multiplies with
another number
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Concept RIO Factors and Products
EXAMPLE
2 x 3 6
Multiplication symbol
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Concept RIO Factors and Products
NON-EXAMPLES
These are not examples of the use of factors and
products. Notice that the number sentences do
not use a multiplication symbol.
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Concept Practice 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
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 INCORRECT
This number sentence is correct because the 15 is
a product it is an answer in the multiplication
equation.
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Fact RIO - Place Value Chart
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 1,000
Hundreds 100
Tens 10
Ones 1
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Fact RIO - Place Value Chart
Thousands 1,000
Hundreds 100
Tens 10
Ones 1
The number 235 can be put into the chart, then I
can figure out how much each digit is worth.
,
2 3 5
Notice that the value increases as we move to the
left
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Fact PracticePlace 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 , 1 5 6 Ones Tens Hundre
ds Thousands 3 , 2 9 8 Ones Tens Hundreds
Thousands 4 , 6 7 2 Ones Tens Hundreds
Thousands
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Process RIO Addition and Multiplication
Multiplication is just a very quick way of adding
numbers together.222222 12
How many twos are in the problem? 6
So a quicker way of saying 222222 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.
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 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 Monday Tuesday Wednesday Thursday Friday Sa
turday
Click for answer
You CAN solve this problem with multiplication!
3 dogs X 7 days in the week 3 X 7 21
Process Practice Addition and Multiplication
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Procedure RIO - How to Multiply by 2-digits
(without regrouping)
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.
Well be using this multiplication problem
3 4 x 2
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Procedure RIO How to Multiply by 2-digits
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Procedure PracticeHow 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
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Summary
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.
T O 2 3 X 2 4 6
You should now be able to tell Ms. Martinez how
many slices of pizza to order for the class by
solving 23 x 2.
Ms. Martinez should order 46 slices!
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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.h
  tml

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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.
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.
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Quiz
Exercise C Solve the following problems. If
necessary, refer to the action table to the right.
T O T O T O 9 2 3 4 4 3 x 1 x 2 x 2
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Reusable Learning Object

• Multiplying 2-digit Numbers
• Maggie Martinez
• Summer 2005