What Is a Fraction?
What a fraction is: equal parts of a whole, what the top and bottom numbers mean, why a bigger bottom means smaller pieces, and where fractions sit on a number line.
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What a Fraction Is
A fraction is part of a whole. Cut the whole into equal pieces, then take some of them.
Formula
| Name | It tells you |
| Denominator (the bottom) | how many equal pieces the whole is cut into |
| Numerator (the top) | how many of those pieces you take |
So of a pizza means: cut it into 8 equal slices and take 3 of them. 5 slices are left.
Common mistake
Pieces that are not equal. A bar cut into 4 uneven bits does not show quarters. Every piece must be the same size.
Bigger Bottom, Smaller Pieces
The bottom number sets the size of each piece. The more pieces you cut, the smaller each one gets.
Worked example
- 1
— Cut a whole into 2 and each piece is half of it. Cut it into 3 and each piece is smaller, because the same whole is shared more ways.
- 2
— Same idea: 6 equal pieces are smaller than 4 equal pieces of the same whole. Bigger bottom, smaller piece.
- 3
— The top equals the bottom: you take all 4 of the 4 pieces, so you have the whole thing.
- 4
— The top is bigger than the bottom. Split it: 4 quarters make one whole, and 1 quarter is left over.
- 5
— Swap for 1. So is more than one whole: 1 whole and 1 quarter.
Key idea
A fraction is also a division: means . Share 3 cakes between 4 people and each gets three quarters.
Common mistake
Thinking is bigger than because 6 is bigger than 4. Six people sharing get smaller slices than four.
Fractions on a Number Line
The 1-mark question: "Mark on the number line." Fractions are numbers, so they have a place on the line.
Worked example
- 1
— Split the space from 0 to 1 into 5 equal gaps, because the bottom number is 5. Each gap is one fifth.
- 2
— Start at 0 and move 3 gaps, because the top number is 3. Mark the point there.
- 3
— Check it: halfway is 2.5 of the 5 gaps. 3 gaps is a little more, so the mark should sit just right of the middle.
- 4
— After all 5 gaps you reach 1, because five fifths make one whole.
- 5
— Keep counting past 1: 7 gaps is 5 gaps to reach 1, then 2 more. So sits at .
Common mistake
Counting the marks instead of the gaps. Start at 0 and count the spaces between the marks.
Write It as a Fraction
Exams often ask “what fraction is shaded?” or “what fraction of 2 hours is 50 minutes?”. The whole always goes on the bottom.
1. What fraction is shaded? A rectangle is cut into 12 equal squares and 4 are shaded.
Worked example
- 1
— Count every square, shaded or not. That total is the whole, so it goes on the bottom.
- 2
— Count only the shaded squares. That is the part, so it goes on top.
- 3
— Part over whole.
- 4
— Divide top and bottom by 4, the biggest number that goes into both. Exams usually want the simplest form.
2. Different units. What fraction of 2 hours is 50 minutes?
Worked example
- 1
— Put both amounts in the same unit first. 1 hour is 60 minutes, so 2 × 60 = 120.
- 2
— The amount after “of” is the whole, so 120 goes on the bottom. The part, 50, goes on top.
- 3
— Divide top and bottom by 10. 5 and 12 share no other factor, so this is the simplest form.
Memory trick
Part on top, whole on the bottom, same units.
Common mistake
Writing . Hours and minutes do not mix. Change 2 hours into 120 minutes first.
Which Method? Read the Question
Use the words in the question to pick what to do.
| You see | You do |
| What does the bottom number mean? | how many equal pieces |
| What does the top number mean? | how many pieces you take |
| Which is bigger, one third or one fifth? | bigger bottom, smaller piece |
| Mark it on a number line | bottom sets the gaps, top counts them |
| What fraction is shaded? / What fraction of A is B? | part on top, whole on the bottom, same units |
| Shade or find a fraction of an amount | Fractions of an Amount |
| Same fraction, different numbers | Equivalent Fractions |
Key idea
Quick check: if the top is smaller than the bottom, the fraction is less than one whole.
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