Fraction Addition Concepts
Understand addition and subtraction of fractions as joining and separating parts; decompose a fraction into a sum of fractions with the same denominator in more than one way
What a learner can do afterwards
- Show that 3/8 = 1/8 + 1/8 + 1/8 and also 3/8 = 1/8 + 2/8
- Write two different decompositions of 5/6
- Use a visual model to justify a decomposition of 2 1/8 into whole-number and fraction parts
The lesson
You already know how to add fractions that have the same denominator. Now think of a fraction as a group of same-size pieces. Adding pieces together is joining them into one group. Taking pieces away is separating them.
Priya has 5/6 of a garden left to plant and wants to split the work over two days. She could plant 1/6 on day one and 4/6 on day two: 1/6 + 4/6 = 5/6. Or she could split it as 2/6 and 3/6: 2/6 + 3/6 = 5/6. Same total, two different splits.
A mixed number like 2 1/8 is a whole-number part plus a fraction part: 2 1/8 = 2 + 1/8. Picture two full bars, then one small piece of a third bar.
A fraction can be split into same-denominator pieces in more than one way, and joining or separating those pieces is what addition and subtraction of fractions really means.
Watch it
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.