# Wikijunior:Introduction to Mathematics/Counting

## Counting from one to ten.Edit

You learn to count from one to ten by repetition. You also learn to recognize the relationship between numerals and number words. You learn to count backwards from ten to one. You learn to identify from one to ten objects. One to five objects you should identify on sight (without counting). You should be able to do the same with six to ten objects that are grouped in certain patterns.

Most people learn this skill when very young, but just as there are adults, some very successful, who cannot read or write, there are adults who have never mastered this number skill. It is essential to further progress in mathematics.

If an adult does not know how to read at an adult level, I advise them to read aloud to children. If you are an adult, and are unsure about numbers, teach numbers to a child.

The first skill in this section is to be able to say aloud, as you might say the lyrics of a song you heard often:

one two three four five six seven eight nine ten

Practice this, hundreds of times if necessary, until it haunts you, until if someone says "six" you automatically think "seven eight nine ten".

Practice writing the numerals, and saying their names aloud. The first ten numerals are

1 2 3 4 5 6 7 8 9 10

If you are not already perfect at this, write these ten numerals on ten separate sheets of paper, and practice pulling one out at random and saying the name of the number. If you are teaching this skill to a child, make a set of flash cards with the word on one side and the numeral on the other.

The next skill in this lesson is to count down from ten. As with counting, just repeat until you know by heart:

ten nine eight seven six five four three two one.

When you have done this, if you are thinking in terms of "counting down" and someone says "seven" you should automatically think "six five four three two one".

The final skill in this lesson is recognition of "how many objects" there are in a group of one to five objects. Practice this until it becomes automatic. As soon as you see a group of one to five objects, you should know, without thinking about it, how many objects are in the group. If this does not come easy for you, practice with small groups of objects at home until you can do it without counting or even thinking. Then move on to groups of six to ten objects. You do not need to automatically recognize how many objects are in these groups unless the groups are arranged in one of the following patterns, but you should recognize, on sight, each of the following patterns:

@@@ @@@ six objects

@@@ @@@@ seven objects

@@@@ @@@@ eight objects

@@@ @@@ @@@ nine objects

@@@@@ @@@@@ ten objects

Once you have learnt the numbers one to ten, you can practice identifying a bigger number out of two given numbers. For example:

- (2,3) - 3 is bigger
- (6,4) - 6 is bigger

## Counting from eleven to twenty.Edit

In some languages, Chinese for example, the number words from eleven to twenty follow the same pattern as the number words from twenty to thirty, but this is not the case in English, and so you need to memorize the number words from eleven to twenty. Repeat the following until you know it by heart:

eleven, twelve, thirteen, fourteen, fifteen, sixteen, seventeen, eighteen, nineteen twenty

You do not need to learn this list backwards.

The numerals eleven to twenty are

11 12 13 14 15 16 17 18 19 20

You need to associate the numeral with the word so that the sight of either brings to mind the other. Use flash cards.

You also need to think of 11 as ten plus one, 12 as ten plus two, and so on, so that in mastering these number words, you also begin to master addition facts.

## Counting to twenty by twos.Edit

The next skill is to count "by twos" from two to twenty. When you count by twos, each number is two more than the previous number. This kind of counting is sometimes called "skip counting" Memorize:

2 4 6 8 10 12 14 16 18 20

Say it over and over until you know it by heart.

Note that the word "twos" is plural, not possessive, and does not take an apostrophe.

## Counting to one hundred by tens.Edit

The next skill is counting by tens from ten to one hundred. Each number is ten more than the previous number. Memorize:

ten, twenty, thirty, forty, fifty, sixty, seventy, eighty, ninety, one hundred.

Note in particularly, the spelling of "forty". That spelling does not make any sense, considering the way we spell "fourth" and "fourteen", but we must follow the dictionary when it comes to spelling.

Learn to match the names and the numerals until it becomes second nature:

10, 20, 30, 40, 50, 60, 70, 80, 90, 100

Notice that while the spelling (in the case of forty) does not follow a pattern, the numerals do follow a pattern. That is, if you knew ten, twenty, and thirty, that would not help you guess "forty". But if you knew 10, 20, and 30, you could easily guess 40. This is the wonderful thing about mathematics. It follows patterns, so that after you learn just a few things, you can then guess correctly many more things. This is why you can learn, in less than a year, what it takes twelve or more years to learn in school. School usually uses too much memorization. In this book, you will memorize only what must be memorized, and learn the rest by seeing the pattern.

You need to have an idea of how many one hundred is. One hundred is ten tens. Gather one hundred objects on a table, in ten groups of ten. (Really do this. Don't just think about doing it, do it.) One hundred is big, but not too big. I would never ask you to gather a million objects. It would take days, and they wouldn't fit on the table.

## Counting to one hundred by twenties.Edit

Memorize:

20 40 60 80 100

The main reason this is important is that the twenty dollar bill is in common use in the United States.

Remember, memorize means memorize. Yes, you could figure out how to count by twenties. That isn't good enough. This basic stuff you need to be able to do without thinking, while you are thinking about something more important. Be sure you can count by twenties while you are washing dishes or talking on the telephone. Be sure you could count out the values of five twenty dollar bills while carrying on a conversation with the bank teller.

## Counting to one hundred by ones and by fives.Edit

After twenty, all the whole numbers follow a pattern. After you know that 87 is read "eighty seven" and means eighty plus seven, you know almost all the number words you will ever need to know. I haven't counted them, but I would guess that in all the rest of this book you will need to learn less than a dozen more number words. In other words, you've already learned the most important part of mathematics! Now, if you've never done it before, count out loud to 100. You don't need me to tell you how. You can figure it out for yourself. Now count by fives to 100. I'm not going to tell you how to do it. Find the pattern.

## Who's on first?Edit

When a number word is used as an adjective instead of as a noun, it changes. If the number word is one, two, or three, or if the number word ends in one, two, or three, as does two hundred fifty-three, then "one" becomes "first", "two" becomes "second", "three" becomes "third". When the numbers are given using numerals instead of words, we use superscripts: 1^{st}, 2^{nd}, 3^{rd}, pronounced "first", "second", "third". All other number words and numerals add "th" when used as an adjective, thus, "fourth", "fifth", "sixth", "seventh", "eighth", "nineth", "tenth", "eleventh", and so on. Note that "fourth", the adjective form of "four", is not the same word as "forth", meaning "forward". Also note the odd spelling and pronunciation of "fifth" (the second "f" is silent), and the fact that "eighth" does not have a double "t".

When a number word is used as an adjective, it is sometimes called an "ordinal" number, when used as a noun, a "cardinal" number. Thus 3^{rd} is the third ordianal, while 3 is the third cardinal.

## ZeroEdit

The number 0, read "zero", stands for "none at all". In the room where you are reading this, there are zero pink elephants. Note that the numeral for 0 is slightly narrower than the letter capital O. Sometime, people draw a slash through their zeroes, so as not to mix them up with O's. (They can also sometimes draw a slash through capital Z so as not to mix it up with 2.)

## DigitsEdit

In our number system, which originated in India and has now spread everywhere in the world because it is so useful, every whole number, no matter how large, can be written with just ten digits. The digits are:

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

In other countries, people sometimes write the digits differently, but they still use ten digits.

## Thousand, million, billion, trillion.Edit

A thousand is ten hundreds. The number 1572 is "one thousand five hundred seventy-two". Notice that numbers between twenty-one and ninety-nine, except for every tenth number (thirty, forty, fifty, and so on) are written with a hyphen.

Starting with ten thousand, numerals are written with commas, so "ten thousand fifty-six" is written 10,056. Notice that the 0 in 056 means that there are no hundreds in this numeral. In this case, the 0 is called a "place holder". Every three digits in a large number are set off by a comma, starting from the right. If a numeral has one comma, it is read "thousand", if a number has two commas the first comma is read "million", if three commas, the first is read "billion", at least in the United States, while in the United States, if a number has four commas, the first is read "trillion". Other countries have different number names. In practice, very large numbers are often read just by reading their digits. Thus we might read 10,056 as "one zero zero five six".

A million is a thousand thousands. It is a very big number, but a billion is much bigger. The word "billion" is used in two different ways. In America, "billion" means a thousand million. In most of the rest of the world, "billion" means a million million. When communicating large numbers across national borders, it is better to use numerals than words.

In America, a "trillion" means a thousand American billions. In most of the rest of the world, a "trillion" is not used at all.

There are words for even larger numbers, but they are seldom used, so we won't bother with them. For large numbers, just read off the digits. One interesting word for a very large number is the word "google". Look it up if you want to know what number it stands for.

It is hard to grasp the size of very large numbers. Here is one way to put them in perspective. As I write this, the national debt of the United States is about nine trillion dollars ($9,000,000,000,000), while the population of the United States is about three hundred million (300,000,000). If the United States spends a million dollars, then each person's share is less than one cent. If the United States spends a billion dollars, then each person's share is between $3 and $4. If the United States spends a trillion dollars, then each person's share is more than $3,000. As you can see, there is quite a difference between a million, a billion, and a trillion.

## The natural numbersEdit

The whole numbers, starting with 1, 2, 3, ..., are called the "natural numbers". The dot dot dot is called an "elipsis" and means "and so on". By the way, an elipsis always has three dots, no more, no less. The natural numbers go on without end. The word we use for "without end" is "infinity". There are infinitely many natural numbers. We could never write them all.

People do not agree on whether to include 0 in the natural numbers. Older authors often do include 0, thus: 0, 1, 2, ..., while more modern authors generally put zero in a class by itself, and start the natural numbers with 1.