Why can't I subtract straight across?
Leo worked out 3/4 - 1/3 by subtracting the tops and adding the bottoms, writing 2/7. The pieces were different sizes.
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2 lessons for “Subtracting fractions”
Why write 7/4 as 1 and 3/4?
Both forms describe exactly the same amount. One is better for seeing how much it is, and the other is better for calculating with it.
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Why do I flip the second fraction?
Amara shared 1/2 of a sandwich into 2/3-sized portions and wrote 1/3. She multiplied by 2/3 instead of flipping it first.
Try this lessonWhy can’t I add the denominators?
Before you add pieces, make sure they are the same size. The denominator names the pieces; the numerator counts how many you have.
Try this lessonWhy do I multiply straight across?
Sam computed 1/2 * 2/3 and wrote 3/5. He added the top numbers and the bottom numbers, which is how you combine, not how you multiply.
Try this lessonWhy does 18/24 turn into 3/4?
The fraction looks different and describes the same amount. The rule that allows this is the same rule that makes adding fractions possible at all.
Try this lessonWhy is 3/5 the same as 60%?
Three names for the same amount, and one short chain that gets you between them. The confusion is rarely the arithmetic — it is which direction you are going.
Try this lessonWhy is 5/8 smaller than 2/3?
Five is a bigger number than two and eight is a bigger number than three, yet five eighths is the smaller amount. Bigger numbers on the page are smaller pieces of the whole.
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