
My Foolproof Method for finding Factors
Easily know when you've found ALL the factors!
Students have to learn how to find the factors of a number because several tasks in working with fractions require students to find the factors of numbers. Thinking of some of the factors of a number is not hard. What is hard is knowing when you have thought of ALL the factors. Here is a foolproof, systematic method I recommend: starting from 1 and working your way up the numbers. This is what students practice in the
Rocket Math Factors program
(part of the Universal Subscription)
.
How to find all the factors of numbers
Always begin with 1 and the number itselfthose are the first two factors. You write 1 x the number. Then go on to 2. Write that under the 1. If the number you are finding factors for is an even number then 2 will be a factor. Think to yourself "2 times what equals the number we are factoring?" The answer will be the other factor.
Go on to 3. Think to yourself "3 times what equals the number we are factoring?" Then you go on to fourand so on.
The numbers on the left start at 1 and go up in value. The numbers on the right go down in value. You know you are done when you come to a number on the left that you already have on the right. Let's try an example.
Let's find the factors of 18.
(Above you see a part of a page from the Rocket Math factoring program.)
 We start with the first two factors, 1 and 18. We know that one times any number equals itself. We write those down.
 Next we go to 2. 18 is an even number, so we know that 2 is a factor. We say to ourselves, "2 times what number equals 18?" The answer is 9. Two times 9 is 18, so 2 and 9 are factors of 18.
 Next we go to 3. We say to ourselves, "3 times what number equals 18?" The answer is 6. Three times 6 is 18, so 3 and 6 are factors of 18.
 Next we go to 4. We say to ourselves, "4 times what number equals 18?" There isn't a number. We know that 4 times 4 is 16 and 4 times 5 is 20, so we have skipped over 18. We cross out the 4 because it is not a factor of 18.
 Next we go to 5. We might say to ourselves, "5 times what number equals 18?" But we know that 5 is not a factor of 18 because 18 does not end in 5 or 0 and only numbers that end in 5 and 0 have 5 as a factor. So we cross out the five.
 We would next go to 6, but we don't have to. If we look up here on the right side we see that 6 is already identified as a factor. So we have identified all the factors there are for 18. Any more factors that are higher we have already found. So we are done.

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4th grade Rocket Math Students practicing
St. Rose of Lima School, Warwick, RI
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The Rocket Math song (tune of Rocket Man)
At a school assembly in an elementary school in the Bethel School District in Oregon, teachers and students celebrated by performing the Rocket Math songwhose lyrics they wrote!





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Can you explain the "filing cabinet on the web?"
Jo asks:
Can you explain the "filing cabinet on the web" a little more? Is this a place a teacher can print copies for the class or does each student have to have subscription?
Dr. Don answers:
A subscription gives you access to our "filing cabinet on the web." This is a place on the web where we keep all the worksheets and a teacher goes there to print out what is needed. You just click on what you want and print it out. Each operation has its own drawer. Each drawer looks like this:
There are five drawers that can be accessed with the
$29 basic subscription: Forms and Information, Addition, Subtraction, Multiplication, Division.
But wait there's more!
There are currently 8 more drawers, the contents of which are only available to those who have the
$49 Universal subscription. Click on the Universal Subscription page and you can get more information on each of the 8 programs added in the Universal Subscription:
 Rocket Writing for Numerals,
 Skip Counting,
 Add to 20,
 Subtract from 20,
 Multiplication 10s, 11s, and 12s,
 Division 10s, 11s, and 12s,
 Factors, and
 Integers.
You can preview (before you buy) the whole subscription site here:
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Thank you for your interest in Rocket Math. I created it to help students be more successful, gain confidence and enjoy math more. Let me know how else I can help. Feel free to call me with any questions you have or send me an email to
don@rocketmath.com
Sincerely,
Dr. Don
Rocket Math
phone (888) 4884854





