Curriculum placement
Grade 5. This describes the skill, not a learner estimate.
Adding and subtracting unlike fractions
Add and subtract unlike-denominator fractions
Problem types
- Add fractions
- Subtract using a shared unit
- Measure a fractional gap
- Estimate with 0, one half and 1
- Add and subtract three or four unlike fractions
- Subtract the sum of two measures from a total
Builds on
- Generating equivalent fractions
- Adding and subtracting like fractions
- Comparing fractions with benchmarks · Useful idea
Deciding which of two fractions is greater with a common denominator is the same rewriting that adds and subtracts unlike fractions, and it lets a sum or difference be estimated from the nearest of 0, one half and 1.
- Greatest common factor and least common multiple · Useful idea
The least common multiple of two denominators is the least common denominator for adding unlike fractions.
- Adding and subtracting mixed numbers · Useful idea
Adding mixed numbers adds the whole parts and the fractional parts, regrouping when the fractional sum exceeds 1.
Leads to
- Fraction operations on a line plot
- Adding and subtracting signed numbers
- The addition rule for probability · See it applied
The probability of one event or another adds their probabilities, which are fractions.
- Operations on rational expressions · Extend the idea
Finding a common denominator to add fractions is the same step used to add rational expressions.
Related skills
- Fluent decimal arithmetic · Related idea
A fraction with a denominator such as 2, 4, 5 or 10 has an exact decimal form, so a sum that mixes both can be done in either form.
- Tenths and hundredths as decimals · Shared foundations
- Multiplying fractions · Shared foundations
- Adding and subtracting from a line plot · Shared foundations
Open the interactive map to explore lessons and skill connections.