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Converting Fractions to DecimalsPowerPoint Presentation

Converting Fractions to Decimals

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## PowerPoint Slideshow about ' Converting Fractions to Decimals' - ginger-lyons

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Discussion

- Who can explain what a fraction is?
- Who can explain what a decimal is?
- Can you find a decimal that is equivalent to ¼?
- What method did you use to find this?

Egyptian Fractions

- The Egyptians of 3000 BC had an interesting way to represent fractions.Although they had a notation for 1/2 and 1/3 and 1/4 and so on (these are called reciprocals or unit fractions since they are 1/n for some number n), their notation did not allow them to write 2/5 or 3/4 or 4/7 as we would today. Instead, they were able to write any fraction as a sum of unit fractions where all the unit fractions were different.
- A fraction written as a sum of distinct unit fractions is called an Egyptian Fraction.

Why use Egyptian Fractions Today?

- For two very good reasons:
- The first reason is a practical one. Suppose you have 5 sacks of grain to share between 8 people, so each would receive 5/8 of a sack of grain in terms of present-day fractions. How are you going to do it simply, without using a calculator? You could try pouring the 5 sacks of grain into 8 heaps and, by carefully comparing them, perhaps by weighing them against each other, balance them so they are all the same! But is there a better way? We will see that using unit fractions makes this easier.
- The second reason is that it is much easier to compare fractions using Egyptian fractions than it is by using our present-day notation for fractions! For instance: Which is bigger: 5/8 or 4/7?
- but remember - you are notallowed to use your calculator to answer this! Again unit fractions can make this much simpler.
- On this page we see how both of these work in Egyptian fractions.

Video

Lets watch a video to preview how to convert fractions to decimals, the Egyptian way!

Converting Fractions to Decimals

- To convert a Fraction to a Decimal manually, follow these steps:
- Step 1: Find a number you can multiply by the bottom of the fraction to make it 10, or 100, or 1000, or any 1 followed by 0s.
- Step 2: Multiply both top and bottom by that number.
- Step 3. Then write down just the top number, putting the decimal place in the correct spot (one space from the right for every zero in the bottom number)

Method #1: Converting with Proportions

- Example # 1: Express 3/4 as a Decimal
- Step 1: We can multiply 4 by 25 to become 100
- Step 2: Multiply top and bottom by 25
3 = 75

4 100

Example # 1 continued….

- Step 3: Write down 75 with the decimal place 2 spaces from the right (because 100 has 2 zeros);
- Answer = 0.75
- Can you explain what we just did?
- Try to express ¼ as a decimal using method # 1.

Method #2: Convert by Dividing

- Example #1: to write 5/8 as a decimal, we need to calculate 5 ÷ 8: 0.625
8 √ 5.000

So = 0.625 as a decimal.

- Try this example: write 4/5 as a decimal using division (method #2).

- Sort your skittles into groups by color.
- Find the fraction of each color.
- Convert your fractions into a decimals.
- Record your data on chart paper.
- Compare and discuss with the class.

Lets Practice!!

- We are going to use this website to fish out some fractions and decimals.
- Lets see how well you understand this lesson.
- Go to www.iknowthat.com
- Select “Math” in the left margin
- Select “Fishy Fractions”
- Select “Fractions and Decimal Match”

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