Virginia SOL 2.CE.1.g
The Standard
Determine the missing number in an equation (number sentence) through modeling and justification with addition and subtraction within 20 (e.g., 3 + = 5 or + 2 = 5; 5 – = 3 or 5 – 2 = ).
Virginia Standards of Learning for Mathematics · The student will recall with automaticity addition and subtraction facts within 20 and estimate, represent, solve, and justify solutions to single-step and multistep problems, including those in context, using addition and subtraction with whole numbers where addends or minuends do not exceed 100.
Teacher's field guide
What This Standard Means
What Students Need to Do
- Students find an unknown number in an addition or subtraction equation within 20. They use objects, drawings, or number lines and explain why the missing value makes the equation true.
What Mastery Looks Like
- Students find the unknown whether it appears at the beginning, middle, or end of an equation. They model their thinking with counters, drawings, or a number line and verify the value by substitution.
Common Misconceptions
- Students may treat the blank as an equal sign or assume it always comes at the end. They may combine the visible numbers without checking the operation or subtract in the wrong order.
How to Assess It
- Give students □ + 6 = 14 and 15 - □ = 9. Ask them to solve each, draw a model, and write one sentence explaining their reasoning.
Lesson moves
Ways to Teach It
Give pairs 20 counters and equation cards, then have them build each equation and place the missing number in the blank.
Ask students to explain in writing how addition can help solve 13 - □ = 8.
Play Missing Number Match by pairing equation cards with answer cards, requiring students to prove each match with a number line.
Present a story about 12 apples with some eaten, then connect the remaining amount to 12 - □ = 7.
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Printable 2.CE.1.g Worksheet
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Related Standards
- K.CE.1
The student will model and solve single-step contextual problems using addition and subtraction with whole numbers within 10.
- 1.CE.1.e
Solve addition and subtraction problems within 20 using various strategies (e.g., inverse relationships: if 9 + 3 = 12 then 12 - 3 = 9; decomposition using know...
- 2.CE.1.h
Use inverse relationships to write all related facts connected to a given addition or subtraction fact model within 20 (e.g., given a model for 3 + 4 = 7, write...
- 2.CE.1.d
Demonstrate fluency with addition and subtraction within 20 by applying reasoning strategies (e.g., doubles, near doubles, make-a-ten, compensations, inverse re...
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