| Sometimes we write fractions in a different way. | ||
| Instead of drawing a line, we use two dots. | ||
| We get something like this: | ||
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| But it still means exactly the same thing: | ||
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| The difference is, | ||
| we usually use the line when we have one thing | ||
| that is chopped up into pieces. | ||
| Like a pizza. | ||
| We use the 2 dots (called a colon) when we are talking about | ||
| some of the members of a group | ||
| or comparing two different things. | ||
| The 2 dots way of writing things is sometimes called a ratio and sometimes called a proportion. But it is NEVER called a fraction. | ||
| Example: | ||
| Say that there are 10 people in a math class. | ||
| 3 of them got A's on the last test. | ||
| So we say "3 out of 10 got A's on the test." | ||
| We would write this as: | ||
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3:10 |
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| More Examples: | ||
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3 out of 9 players on the team are over 6 feet tall. |
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3:9 |
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| 2 out of 3 kids in the family go to Jefferson Middle School. | ||
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2:3 |
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| Remember, the part on the right is the whole thing. | ||
| We could have said that last one as: | ||
| 2 out kids in the family go to Jefferson Middle School. | ||
| The other kid in the family is too young for school. | ||
| It is the same problem, | ||
| but you have to figure out how many kids are in the family. | ||
| There is one way these things work just like fractions. | ||
| We can reduce them the same way. | ||
| Example: | ||
| Say we had this ... | ||
| 4 out of 10 people in the class are boys: | ||
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4:10 |
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| Can we show the same ratio with smaller numbers? | ||
| Let's see ... | ||
| First, find the prime factors of 4 and 10: | ||
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| So we can write our ratio like this: | ||
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2 × 2 : 2 × 5 |
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| If everything is multiplied together on each side (it is). | ||
| If the same number shows up on both sides (it does). | ||
| We can change them both to 1's just like we did with fractions. | ||
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| Try another one ... | ||
| Example: | ||
| Three of twelve: | ||
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copyright 2005 Bruce Kirkpatrick |
