Curriculum placement
Grade 1. This describes the skill, not a learner estimate.
Finding a missing number
Find an unknown in an addition or subtraction equation
Problem types
- Find what was added
Builds on
- The meaning of the equal sign
- Subtracting within 20
- Number bonds to 10 · Earlier idea
A number bond shows a whole and its two parts. When one part is unknown, the missing addend is the whole minus the known part.
Leads to
- Solving one-step equations
- Two-step word problems · See it applied
Finding how many were there at the start of a story is an unknown addend: start plus change equals end.
- Missing factors and quotients · Extend the idea
An unknown addend is the whole minus the known part. An unknown factor is the product divided by the known factor.
- Finding elapsed time · See it applied
Start time plus elapsed time equals end time, so an unknown elapsed time or start time is an unknown addend.
Related skills
- Subtracting within 10 · Related idea
Subtraction and addition undo each other: 5 - 2 = 3 tells you that 2 + 3 = 5, so an unknown addend is found by subtracting.
- Addition and subtraction facts · Shared foundations
- Equal multiplication and division equations · Shared foundations
- Subtracting within 100 · Shared foundations
Open the interactive map to explore lessons and skill connections.