Grade 1 · Operations · MAT-01-OPS-010
Subtraction Word Problems Within 20
Identify take-away, separating, and comparison subtraction situations within 20.
Learning objectives
What you should be able to do
- Identify take-away, separating, and comparison subtraction situations within 20.
- Represent subtraction word problems with drawings, equations, and labeled answers.
- Explain what the difference means in the context of the story.
Prerequisite check
Make sure the foundation is ready.
Checks computation readiness.
Checks contextual meaning.
Learn
Build the idea from meaning, not memorization.
Subtraction problems can represent different relationships
Take-away problems remove part of a starting whole. Comparison problems ask how many more or fewer one quantity is than another. Missing-part problems ask for an unknown part of a known whole.
Model before computing
For 15 birds with 6 flying away, draw or build 15, remove 6, and count 9. For comparison, align or pair quantities to see the difference.
The difference answers a contextual question
In 15−6=9 birds, 9 means nine birds remain. In a comparison of 15 and 6, a difference of 9 means one quantity has nine more than the other.
Choose subtraction because of the structure
Do not rely on a single keyword. Decide whether the problem starts from a whole, removes a part, asks for a missing part, or compares two quantities.
Interactive math lab
Change it. See what stays true.
Equation Balance
Adjust both sides. Equality means both expressions have the same value.
Balanced: both sides have equal value.
- classify structure
- build model
- choose equation
- label difference
Worked examples
Twenty different ways to see the concept work.
12 birds; 4 fly away.
12−4=8 birdsTake-away.
15 blocks; 6 put away.
15−6=9 blocksRemove part of whole.
18 balloons; 9 pop.
18−9=9 balloonsHalf remain.
14 cookies; 5 eaten.
14−5=9 cookiesTake-away.
17 pencils; 7 given away.
17−7=10 pencilsRemove seven.
11 apples; 3 used.
11−3=8 applesDifference is remainder.
16 students; 4 leave.
16−4=12 studentsStarting whole decreases.
20 counters; 8 removed.
20−8=12 countersTwelve remain.
13 books; 2 borrowed.
13−2=11 booksCount back two.
19 fish; 10 swim away.
19−10=9 fishRemove one ten.
15 red vs 11 blue. How many more red?
15−11=4Comparison difference.
9 cats vs 6 dogs. How many fewer dogs?
9−6=3Compare counts.
18 points vs 14 points. Difference?
418−14=4.
Whole 12; part 7 known. Other part?
12−7=5Missing-part subtraction.
Which equation matches 16 toys with 5 removed?
16−5=11Start with whole and subtract removed part.
What does 11 mean in 16−5=11 toys?
11 toys remainInterpret answer.
How can pairing show 8 vs 5 difference?
Three unmatched in larger set8−5=3.
Why can 'how many more' be subtraction?
It asks for the gap between quantitiesComparison finds difference.
Explain 14−6 with a drawing.
Draw 14, cross out 6, count 8Model matches take-away.
Explain difference between take-away and comparison.
Take-away changes one set; comparison measures gap between two setsBoth can use subtraction.
Practice
Guided practice with hints
0113 birds; 5 leave.
Hint: Build/draw 13 and remove 5.
Answer: 8 birds
0217 blocks; 9 put away.
Hint: Use think-addition 9+?=17.
Answer: 8 blocks
0312 red vs 8 blue. How many more red?
Hint: Find the difference.
Answer: 4
04Whole 15, known part 6.
Hint: Subtract known part.
Answer: 9
05Why might 'more' still lead to subtraction?
Hint: If question asks how many more one has than another.
Answer: Comparison.
06What unit belongs on the answer?
Hint: Use the story noun.
Answer: Objects/people/points etc.
Practice
Independent practice
0114−5 story remainder
Answer: 9
0216−7 story remainder
Answer: 9
0318−8 story remainder
Answer: 10
0412 vs 9 difference
Answer: 3
0517 vs 11 difference
Answer: 6
06Whole 13, part 4, missing part
Answer: 9
07What does difference mean in comparison?
Answer: The gap between quantities.
08What should final answer include?
Answer: Number and context/unit.
Common mistakes
Learn to catch the error, not just the answer.
Recognize comparison and missing-part structures too.
Identify whole/larger quantity and the part or smaller comparison amount.
State whether it means remaining amount, missing part, or comparison gap.
Applications & challenge
Use the idea beyond a single exercise.
Applications
- Find how many items remain after some are used.
- Compare two small counts to find how many more/fewer.
Challenge problems
Write a comparison problem for 15−9.
Any story comparing quantities 15 and 9 with a difference of 6.
Write a take-away problem for 15−9.
Any story starting with 15, removing 9, leaving 6.
Why can the same equation model two different story structures?
The numerical relationship can be the same even when context meaning differs.
How can addition check a subtraction word problem?
Add the difference/remainder and removed or smaller part to reconstruct the whole/larger amount.
Flashcards
Retrieve it from memory.
Flashcards
Card 1 of 4
Game mode
Story Detective: Subtract
Classify a subtraction story, model it, and solve within 20.
Practice
Mastery check
0115 birds, 6 leave
Answer: 9 birds
0218 blocks, 8 removed
Answer: 10 blocks
0314 vs 9 difference
Answer: 5
04Whole 12, part 5
Answer: 7
05What is a comparison problem?
Answer: It asks for the difference between two quantities.
06Why not rely on keyword 'more'?
Answer: It can appear in comparison problems solved by subtraction.
07What can difference mean?
Answer: Remainder, missing part, or comparison gap.
08How check subtraction?
Answer: Use related addition.
Terminology
Words to know
- take-away problem
- A situation where part of a starting whole is removed.
- comparison problem
- A situation asking for the difference between two quantities.
- missing part
- An unknown component of a known whole.
- difference
- The result of subtraction.
Continue learning
Connected concepts
Curriculum references
Standards and instructional references
California Common Core State Standards for Mathematics — Grade 1 Operations & Algebraic Thinking
Grade 1 addition/subtraction within 20, word problems, and equations with unknowns.