Unit 1: Common Fractions
Topic C: When to Use a Fraction or a Decimal
Sometimes you need to decide to write or say a number as a fraction or a decimal. We usually choose the most common method which is usually the easiest way to say something. It may seem to you that nothing is easy at this moment, so here are some tips.
Money
When we talk about money, we almost always talk about a part of a dollar.
Example: Two dollars and fifteen cents is two whole dollars and fifteen parts of one more dollar.
$2.15 or [latex]\$2\tfrac{15}{100}[/latex] – which of these ways of writing money is more common or easier to you?
We usually write or talk about money in decimals:
- Example 1: $2.50 (two dollars and fifty cents) instead of [latex]\$2\tfrac{1}{2}[/latex] (two and a half dollars)
- Example 2: $0.50 (fifty cents) instead of [latex]\$\tfrac{1}{2}[/latex] (half a dollar)
- Example 3: $67.30 (sixty seven dollars and thirty cents) instead of $67 (sixty seven dollars and thirty hundredths cents)
But: There is one place where we talk about money as a fraction: The quarter!
A quarter equals $0.25, but we often say “it costs a quarter” as much as we say “it costs 25 cents.”
Really, if we were speaking correctly, it would be a quarter of a dollar, but it gets shortened. Also, we still write $0.25 or 25¢, not [latex]\$\tfrac{25}{100}[/latex] or [latex]\$\tfrac{1}{4}[/latex].
For Other Things: What is Easiest
In most other ways of talking and writing, fractions and decimals are expressed in what seems easiest. This means that you get to say the number in the way you like best.
Example: Saying “six point four grams” may be faster and easier than saying “six and two fifths grams.”
But, saying [latex]\tfrac{3}{4}[/latex] of a tank of gas makes more sense than saying 0.75 of a tank of gas.
Exercise 1
Circle the way that you think a number should be said out loud.
Read the numbers out loud with a friend to help hear them. Remember, that sometimes your answers will be different from the ones in the answer key because you have a different opinion, and that is OK.
- $12.25 or [latex]\$12\tfrac{1}{4}[/latex]
- 51.4 cm or [latex]51\tfrac{2}{5}[/latex] cm
- One million two hundred thousand dollars or one point two million dollars
- 563.56 km or [latex]563\tfrac{56}{100}[/latex] km
- [latex]5\tfrac{7}{10}[/latex] L or 5.7 L
- I ran a tenth of a kilometre or I ran zero point one kilometres
- It weighs five and a half grams or It weighs five point five grams
- [latex]\$39\tfrac{99}{100}[/latex] or $39.99
Answers to Exercise 1
- $12.25
- 51.4 cm
- One point two million dollars
- 563.56 km
- 5.7 L
- I ran a tenth of a kilometre
- Both
- $39.99