Same Denominator
Part of the Factors & Fractions section of Coddy's Pre-Algebra journey. Lesson 28 of 58.
2/9 + 4/9: both fractions count ninths. 2 ninths and 4 ninths make 6 ninths, so the sum is 6/9. Add the tops and keep the bottom.
Why keep the bottom? The denominator names the size of the pieces, and adding does not change their size, just as 2 apples and 4 apples make 6 apples. Adding the bottoms as well would give 6/18, which is 1/3: smaller than 4/9 on its own, so it cannot be the sum.
Finish by simplifying, as in the last chapter: 6 and 9 share a 3, so 6/9 is 2/3. The board will not call a sum finished until it is in lowest terms.
Challenge
Work out 3/8 + 1/8. Add the tops, then write the result in lowest terms.
Try it yourself
Simplify the expression
Test yourselfThis lesson includes a short quiz. Start the lesson to answer it and track your progress.
All lessons in Factors & Fractions
1Factors and Multiples
What a Factor IsFactor PairsDivisibility RulesMultiplesPrime or CompositeRecap: Factors and Multiples4What a Fraction Is
Parts of a WholeFractions on the LineA Fraction of a NumberImproper FractionsRecap: What a Fraction Is7Multiplying Fractions
Top Times TopCancel FirstWhole Times FractionA Fraction of a FractionRecap: Multiplying Fractions10Fractions in Stories
Part of a GroupWhat Is LeftSharing a FractionScaling a RecipeRecap: Fraction Stories2Prime Factorization
Factor TreesUsing ExponentsOne Tree per NumberBigger NumbersRecap: Prime Factorization5Equivalent Fractions
Same Amount, New NameSimplifying FractionsSimplify in StepsComparing FractionsRecap: Equivalent Fractions