Transcript Multiples of Nine - University of Texas at Austin

Multiples of Nine
By:
Krista Smith
Welcome to 4th
Grade!
Teacher
Bell was in a 4th grade class.
She loved her teacher very much.
They learned all sorts of interesting things
about the weather, and history and such.
She enjoyed almost every subject
including writing, science and Texas history.
But when it came to math,
well… that was a different story.
Bell was great at addition
and even pretty good at subtraction.
But there was one thing that she struggled with
and that was multiplication.
12 + 8 = 20
32 - 15 = 17
14 + 19 = 33
45 - 26 = 19
2X4=8
9X6=
?
5 X 6 = 30
10 X 7 = 70
Twos, fives and tens were easy.
She was even pretty good at fours and threes.
But when Bell had to multiply by nines,
she felt like she had a disease.
She would begin to feel quite dizzy
and her tummy began to feel sick.
Even though she had practiced her facts,
the information just wouldn’t stick!
One day the class was doing mad minutes.
It was so hard Bell just hung her head.
Sam noticed her looking sad.
“What’s wrong?” he said.
“Multiplication is just so hard,” Bell explained.
“Especially multiples of nine.”
“Well then I have a trick to teach you,” said Sam.
“You’re going to be just fine.”
“Decide which number you want to multiply by nine
and then hold out your hands.
Count to that number using your fingers
but wait, there’s something else you must understand.”
LEF
T
RIGH
T
“You have to count from left to right
or the trick wont go as planned.
Then fold the finger you counted to down
and the answer will be on your hand.”
“That can’t possibly work,” said Bell.
“It’s just too easy to be true.”
“I’ll prove it to you,” said
Sam.
“Let’s solve 9 X 2!”
Sam held out his hands
And counted to his second finger.
“Now when I fold this finger down,
there the answer will linger.”
9X2=1
1
“The number of fingers to the left
Is the number you’ll put in the tens place.”
9X2=1
8
1
2
5
6
7
8
3
4
“And the number of fingers to the right
represents the ones space.”
9 X 2 = 18
“Oh my goodness!” Bell said,
“I can see it now so clear!
Never again will I struggle with this.
I can multiply by nine without fear!”
.
“Let’s do another example,” said Bell
“I can’t wait to learn some more!”
“Okay,” said Sam, “What do you want to
do?”
Bell suggested 9 X 4!”
“Count 4 over and fold that finger down” said Sam.
“Now which answer will you pick?”
9X4=3 6
2
3
3
1
4
5
6
1
2
“Well there’s 3 to the left and 6 to the right
So that means the answer is 36!”
“Let’s do it again!” Bell exclaimed with glee.
“This time let’s find 8 X 9!”
“Alright,” said Sam. “Do you want me to
help?”
Bell just said, “no, not this time.”
9X8=7 2
2
3
4
7
1
2
1
5
6
,
She counted 8 fingers over and then folded it down
Then she glanced from left to right.
“The answer is 72!” Bell screamed.
Sam just smiled and said, “you’re bright!”
9 X 2 = 18
9 X 3 = 27
9 X 4 = 36
9 X 5 = 45
9 X 6 = 54
9X 7 = 63
9X 8 = 72
9 X 9 = 81
Ever since that memorable day
Bell has done great in math!
All because she found a trick
To multiply by nine in a flash!
TEKS
• 111.16 Mathematics, Grade 4 (b) Knowledge & Skills, (4.4)
Number, operation, and quantitative reasoning. The student
multiples and divides to solve meaningful problems involving
whole numbers. The student is expected to: (D) Use
multiplication to solve problems (no more than two digits times
two digits without technology).
• 111.16 Mathematics, Grade 4 (b) Knowledge & Skills, (4.6)
Number, operation, and quantitative reasoning. The student
uses patterns in multiplication and division. The student is
expected to: (A) Use patterns and relationship to develop
strategies to remember basic multiplication and division facts
(such as patterns in related multiplication and division number
sentences (fact families) such as 9X9=81 and 81/9=9)