# Core Ideas

Do you think you're so hot because you can count to**ten**? Although it doesn't seem like much, you have just mastered the foundations for every number you will encounter in the rest of math (with a few exceptions). All counting and all numbers are based on tens. It's not just a metric system thing. When you start counting, everything starts over when you hit a number with a "0" in the ones column.

# Moving to Fifty

So you count. You get a nice neat list of single digit numbers and a big "10" to finish it off. (0 ,1,2,3,4,5,6,7,8,9,10) What is next? Sorry to disappoint you, but it's very easy. You just start all over again. Do you see the similarity of "0" and "10?" "10" is just a "0" with a "1" in front. If you continue your pattern, the next number in the series will be a "1" with a "1" in front of it. And there you have it. "11."The rest of the numbers follow the same pattern. Next is a "1" with a "2" (12) and then a "3" (13) and so on. The

**series**goes on like this. 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, and then what? You can't go back to "10." That one has already been used. How about moving to the next value in the

**tens**place? How about "20?" It's not really a question. "20" comes after "19." So now you have...

0,1,2,3,4,5,6,7,8,9

10,11,12,13,14,15,16,17,18,19

20, ?

Do you see the pattern? That's it. Just keep adding the next number in the series and you can count to

**infinity**. We're just covering 1 to 50 on this page. So the final set is...

**0,1,2,3,4,5,6,7,8,9 (the ones)**

10,11,12,13,14,15,16,17,18,19 (the tens)

20,21,22,23,24,25,26,27,28,29 (the twenties)

30,31,32,33,34,35,36,37,38,39 (the thirties)

40,41,42,43,44,45,46,47,48,49 (the forties)

50 (and that's it)

10,11,12,13,14,15,16,17,18,19 (the tens)

20,21,22,23,24,25,26,27,28,29 (the twenties)

30,31,32,33,34,35,36,37,38,39 (the thirties)

40,41,42,43,44,45,46,47,48,49 (the forties)

50 (and that's it)

# Looking at the Words

Writing out simple, single-digit numbers is easy for you by now. The numbers between ten and twenty are a little special so we'll hit them first. You know "10" and "Ten" are the same things. 11-19 you will just have to memorize. They have been shortened over the years to make them easier to say.11 is Eleven

12 is Twelve

13 is Thirteen

14 is Fourteen

15 is Fifteen

16 is Sixteen

17 is Seventeen

18 is Eighteen

19 is Nineteen

The rules fall into place after that set. You start to use the "ty" terms (pronounced TEE like the word "tea.") 11 through 20 are called the teens. Then come the

**twenties**,

**thirties**, and

**forties**. When you write out the numbers it is really easy. Start with whatever group of tens you are in, add a dash, and then finish with the number in the ones column. "21" is "Twenty-one." Like this...

21 is Twenty-one

35 is Thirty-five

48 is Forty-eight

## Related Activities

"More or Less" - Comparing Numbers to Thirty (30) Quiz
- Play Activity |
Identify Numbers to Fifty (50) Quiz
- Play Activity |

# Useful Reference Materials

**Wikipedia:**

*https://en.wikipedia.org/wiki/Pre-algebra*

**Encyclopædia Britannica:**

*http://www.britannica.com/topic/mathematics*

**College of the Redwoods:**

*http://mathrev.redwoods.edu/PreAlgText/*