Transcript 2_digit_by_2_digit_mult

Multiplication
Objective:
Multiply a 2-digit number by
a 2-digit number.
Vocabulary
• Product The answer to a multiplication problem.
• Factor A number that is multiplied by another number to find a
product.
Ex: 4 x 6 = 24, 4 and 6 are factors of 24
• Multiply - The act of finding the total number of items in a given
number of groups when each group contains the same number of
items. It is a short cut for addition.
• Array An arrangement that shows objects in rows and columns.
Example:
3 x 4 = 12
3
*** *
*** *
*** *
4
Vocabulary continued
• Set -a group of items.
****
****
• Times - to multiply.
• Multiple - the product of a whole number and
any other number
Ex: the multiples of 3 are 3, 6, 9, 12, 15.
What multiplication number sentence can we
use to represent this set of squares?
What word can we
use to describe the
arrangement of this
set?
6
x 4
------24
6 and 4 are the
factors in this
problem
product
Practice
Find the product.
12
22
31
42
x 3
x4
x4
x3
36
88
124
126
• Demonstration
http://www.dositey.com/muldiv/mul1ml1.htm
• Practice
http://www.dositey.com/muldiv/mul1ss5.htm
Multiplication:
2 Digit by 2 Digit
27
x 38
-------
Multiply the
numbers in the ones
place.
Regroup the 5
above the tens
place.
Put the 6 in the
ones place of the
product.
5
27
x38
------6
Multiply Diagonally
The bottom ones
digit times the top
tens digit.
Then you take this
number and add the
5.
8 x 2 = 16
16+ 5 = 21
Put that answer in
the tens place of the
product.
5
27
x38
------216
Move to the 10’s Digit
When you move to the
bottom tens digit, you
need to write a 0 below
the ones digit of your
answer (because you are
now multiplying by a
ten).
5
27
x38
------216
0
Multiplying by the 10’s
Digit
Multiply diagonally, the
bottom tens digit by the top
ones digit.
3 x 7 = 21
Carry the tens digit above
the tens and write the ones
digit beside the 0 in your
answer.
2
5
27
x38
------216
10
Multiplying by the 10’s
Digit
Multiply straight up and
down in the tens place
3 x 2 = 6…DON’T
FORGET TO ADD THE 2!
6+2=8
Write the answer next to the
1 in your answer.
2
5
27
x38
------216
8 10
ALMOST DONE…now ADD
Now…all you have to do is add
the two lines of your answer!
216
+810
1026
2
5
27
x38
------1
216
+8 1 0
1026
Practice
Find the product.
29
12
26
25
x43
87
x25
60
x65
130
x34
100
+1160
+240
+1560
+750
1247
300
1690
850
Review the vocabulary
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•
•
•
•
•
•
Product
Multiplier
Multiply
Factor
Set
Array
Times
TAKS Preparation
Sample Questions
Mrs. Aljancic bought 14 bags of cookies. There are 17
cookies in each bag. How many cookies did Mrs.
Aljancic buy?
28 cookies
238 cookies
98 cookies
140 cookies
The fourth grade classes had a Browns party in the
cafeteria. There were 25 tables with 37 seats at each
table. How many seats were there in all?
175 seats
750 seats
925 seats
185 seats
Mrs. Bell made 18 packages of cupcakes. There are 12
cupcakes in each package. Which number sentence
shows how many cupcakes Mrs. Bell made?
18 + 12
18 - 12
18 x 12
18 x 2
A decagon has six sides. Mrs. Mason drew 10
decagons. How many sides did she draw?
Decagons
1
2
3
4
Sides
10
20
30
40
50 sides
20 sides
80 sides
100 sides
The table shows how long it takes Mr. McFerren to ride his electric scooter.
Miles
Minutes
2
4
6
15
30
45
If this pattern continues, how many minutes will it take
Mr. McFerren to ride 10 miles?
75 minutes
60 minutes
100 minutes
90 minutes