wunder beta➕ Adding Fractions with Unlike Denominators
Make the bottoms match, then add the tops - the key move for adding unlike fractions.
3
lessons
~15 min
to learn
🔢 Math
subject
Ages 6–12
level
What you’ll learn
- Why the Bottoms Must MatchUnderstand why fractions need the same denominator before adding.Fractions can only be added when the pieces are the same size. A half and a third are different sizes, so 1/2 + 1/3 is not 2/5. The fix is to rewrite both fractions with the same bottom number.
- Finding a Common BottomRewrite fractions with a common denominator and add them.Find a bottom number that both fractions fit into. For 1/2 + 1/3, sixths work: 1/2 = 3/6 and 1/3 = 2/6. Once the bottoms match, add the tops and keep the bottom: 3/6 + 2/6 = 5/6.
- Add and SimplifyAdd unlike fractions and judge whether the sum passes one whole.To add unlike fractions: choose a common bottom, rewrite each fraction, add the tops, and keep the bottom. Examples include 1/4 + 1/2 = 3/4 and 1/3 + 1/4 = 7/12. Some sums stay under one whole while others reach or pass it.
Questions this course answers
Why can't 1/2 + 1/3 be added straight to 2/5?
Halves and thirds are different-sized pieces, so their counts cannot be added until the bottoms match.
A common denominator for 1/4 and 1/2 is?
Halves fit into fourths, so 4 works as the common bottom.
2/3 + 1/6 = ?
Rewrite 2/3 as 4/6, then 4/6 + 1/6 = 5/6.
Grounded in trusted sources
- Khan Academy
- Britannica Kids
- Math is Fun (mathsisfun.com)
- NCTM Illuminations
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