Defining the Whole and Equal Partitions
Defining the Whole and Equal Partitions
Fractions help us describe parts of something. But before we can name a fraction, we must know the whole.
A whole is the entire object, set, length, or amount we are talking about. If the whole changes, the fraction can change too.
Fractions also only work when the whole is split into equal parts. Equal parts are parts that are the same size.
If the parts are not equal, we cannot correctly name them as fractions like halves, thirds, or fourths.
For example, if a sandwich is cut into 2 pieces, but one piece is much bigger than the other, the pieces are not halves. Halves must be 2 equal parts.
Main Idea 1: First define the whole
Sometimes the whole is one shape, like one pizza. Sometimes the whole is a group, like 12 counters. Sometimes the whole is a length, like one ribbon.
We always ask: What is the whole?
- If the whole is 1 cookie, then part of that cookie can be a fraction of 1 cookie.
- If the whole is 3 cookies together, then 1 cookie is only part of the whole group.
- If the whole is a strip of paper, then each equal section is a fraction of that strip.
This means the same piece can have a different name if the whole changes.
Main Idea 2: Fractions need equal partitions
A partition means to split something into parts. A fraction is made when a whole is partitioned into equal parts.
Here are some common equal partitions:
- 2 equal parts = halves
- 3 equal parts = thirds
- 4 equal parts = fourths
- 6 equal parts = sixths
If 1 whole is split into 4 equal parts, each part is one-fourth, written as \(\frac{1}{4}\).
The bottom number tells how many equal parts the whole has. The top number tells how many of those equal parts we are talking about.
So in \(\frac{3}{4}\):
- the 4 means the whole is split into 4 equal parts
- the 3 means we have 3 of those equal parts
Main Idea 3: Equal does not always mean same shape
Equal parts must be the same amount, but they do not always have to look exactly the same.
For example, a rectangle can be split into 2 equal parts up and down, or into 2 equal parts side to side. The parts may look different from another drawing, but if they are the same size, they are equal.
Sometimes shapes are cut in different ways and still make equal parts. What matters is that each part is the same size as the others.
Main Idea 4: Fractions can describe area, sets, and lengths
Fractions are not only for shapes.
- Area model: a shape split into equal parts
- Set model: a group of objects split into equal groups
- Length model: a strip, line, or number line split into equal lengths
In every model, the rule stays the same: first define the whole, then make sure the parts are equal.
Worked Example 1: One shape split into equal parts
A square is split into 4 equal small squares. What fraction is one small square?
Step 1: Define the whole. The whole is 1 square.
Step 2: Count the equal parts. The whole square is split into 4 equal parts.
Step 3: Name one part. One of 4 equal parts is \(\frac{1}{4}\).
Answer: One small square is \(\frac{1}{4}\) of the whole.
We can write:
$$1\text{ part out of }4\text{ equal parts }= \frac{1}{4}$$
Worked Example 2: Unequal parts are not fractions
A circle is cut into 3 pieces, but one piece is large and the other 2 pieces are smaller. Can we say each piece is a third?
Step 1: Ask if the parts are equal.
They are not equal because the pieces are different sizes.
Step 2: Decide if a fraction name works.
No. We cannot call the pieces thirds because thirds must be 3 equal parts.
Answer: No, these pieces are not thirds.
Important: Just counting 3 pieces is not enough. The 3 pieces must be equal.
Worked Example 3: The whole changes the fraction
There are 8 crayons in a box. 4 are blue. What fraction of the crayons are blue?
Step 1: Define the whole. The whole is all 8 crayons.
Step 2: Look at how many equal items are in the whole. Each crayon is 1 equal item in the set.
Step 3: Count the blue crayons. There are 4 blue crayons.
Step 4: Write the fraction. 4 out of 8 crayons are blue, so the fraction is \(\frac{4}{8}\).
Answer: \(\frac{4}{8}\) of the crayons are blue.
Now imagine only the 4 blue crayons are the whole group. Then 1 blue crayon would be \(\frac{1}{4}\) of that new whole.
This shows why defining the whole is so important.
Worked Example 4: Fractions on a length
A strip of paper is split into 5 equal parts. How much of the strip is 2 parts?
Step 1: Define the whole. The whole is the entire strip of paper.
Step 2: Count the equal parts. There are 5 equal parts.
Step 3: Count the parts we have. We have 2 of those parts.
Step 4: Write the fraction. 2 out of 5 equal parts is \(\frac{2}{5}\).
Answer: 2 parts of the strip is \(\frac{2}{5}\) of the whole strip.
How to check if a fraction makes sense
- Ask, What is the whole?
- Ask, Is the whole split into equal parts?
- Count the total number of equal parts.
- Count how many parts you are talking about.
- Write the fraction.
Things to remember
- A fraction names equal parts of a whole.
- You must know what the whole is first.
- Parts must be equal in size or amount.
- If parts are not equal, the fraction name is not correct.
- The whole can be a shape, a set of objects, or a length.
Quick Compare
Look at these two situations:
- A pizza cut into 4 equal slices: each slice is \(\frac{1}{4}\).
- A pizza cut into 4 uneven slices: the slices are not fourths.
The number of pieces alone does not make a fraction. The pieces must be equal.
Summary
Fractions tell about parts of a whole. To name a fraction correctly, you must first know the whole. Then check that the whole is split into equal parts. Equal partitions let us use fraction names like halves, thirds, fourths, and fifths correctly.
Put what you read to the test
You've worked through Defining the Whole and Equal Partitions. Try answering a few questions to see what stuck — and what might deserve a quick reread before you move on.