Kindergarten · Operations · MAT-K-OPS-007
Find Missing Parts Within 10
Find an unknown part when the whole and one part are known within 10.
Learning objectives
What you should be able to do
- Find an unknown part when the whole and one part are known within 10.
- Use objects, number bonds, addition, and subtraction to represent missing-part situations.
- Check a missing part by recomposing the parts into the whole.
Prerequisite check
Make sure the foundation is ready.
Checks part-whole flexibility.
Checks both directions of part-whole reasoning.
Learn
Build the idea from meaning, not memorization.
Sometimes the whole is known but one part is hidden
If there are eight counters altogether and five are visible in one group, the other group must contain three. The whole is 8, the known part is 5, and the missing part is 3.
Use addition to ask 'what joins this part to make the whole?'
The situation can be written 5 + __ = 8. Count on from 5: 6,7,8. Three forward counts were needed, so the missing part is 3.
Use subtraction to find the other part
The same structure can be written 8 − 5 = 3. Start with the whole and remove the known part; what remains is the missing part.
Always check by recomposing
After finding 3, verify that 5 + 3 = 8. A missing-part answer is correct only if the known and missing parts rebuild the original whole.
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.
- hide one part
- count on to whole
- subtract known part
- recompose check
Worked examples
Twenty different ways to see the concept work.
Whole 3, known part 1. Missing part?
21+2=3.
Whole 4, known part 1.
31+3=4.
Whole 4, known part 2.
22+2=4.
Whole 5, known part 2.
32+3=5.
Whole 5, known part 4.
14+1=5.
Whole 6, known part 1.
51+5=6.
Whole 6, known part 4.
24+2=6.
Whole 7, known part 3.
43+4=7.
Whole 8, known part 5.
35+3=8.
Whole 9, known part 6.
36+3=9.
Whole 10, known part 7.
37+3=10.
Complete 2+__=6.
4Count on 3,4,5,6: four steps.
Complete __+4=9.
5Five plus four makes nine.
Complete 8−3=__.
5Removing known part three leaves five.
Complete 10−6=__.
4Four is the other part of ten.
Eight toys total; three are cars. How many are not cars?
53+5=8.
Ten counters total; six are red. How many are another color?
46+4=10.
Check missing part 3 in 5+__=8.
5+3=8The parts rebuild the whole.
A child says 2 is missing in 4+__=7. Is that correct?
No4+2=6; the missing part must be 3.
Explain why 8−5 and 5+__=8 answer the same part-whole question.
Both use whole 8 and known part 5 to find the other part 3.Addition and subtraction describe the same relationship from different directions.
Practice
Guided practice with hints
01Whole 5, part 2. Find the missing part.
Hint: Count on from 2 to 5.
Answer: 3
02Complete 4+__=7.
Hint: Count 5,6,7.
Answer: 3
03Complete __+2=6.
Hint: What plus 2 makes 6?
Answer: 4
04Use subtraction to find the missing part when whole=9 and known part=5.
Hint: Compute 9−5.
Answer: 4
05Check 6+2=8 as a missing-part answer.
Hint: Do the parts equal the whole?
Answer: Yes
06Ten objects total; 7 are visible. How many are hidden?
Hint: Find 10−7.
Answer: 3
Practice
Independent practice
013+__=5
Answer: 2
025+__=8
Answer: 3
03__+4=10
Answer: 6
047−3
Answer: 4
059−6
Answer: 3
06Whole 10, known part 8.
Answer: 2
07Whole 7, known part 0.
Answer: 7
08How do you check a missing part?
Answer: Add the known and missing parts to see whether they equal the whole.
Common mistakes
Learn to catch the error, not just the answer.
Identify which amount is the whole and which part is already known before solving.
When counting on, count only the moves after the known part.
Recompose: known part + missing part must equal the whole.
Applications & challenge
Use the idea beyond a single exercise.
Applications
- Find how many objects are hidden under a cup when the total and visible amount are known.
- Determine how many students are absent when the class total and present count are known, using small numbers.
Challenge problems
If the whole is 10 and one part increases from 6 to 7, what happens to the missing part?
It decreases from 4 to 3.
Why can both addition and subtraction solve a missing-part problem?
They are inverse views of the same part-whole relationship.
Create a story for 3+__=8.
Any story with whole 8, known part 3, and missing part 5.
A missing part answer is 4 for whole 9 and known part 6. How can you disprove it?
6+4=10, not 9; the correct missing part is 3.
Flashcards
Retrieve it from memory.
Flashcards
Card 1 of 6
Game mode
Hidden Part
Infer how many objects are hidden when the total and visible part are given.
Practice
Mastery check
01Complete 2+__=5.
Answer: 3
02Complete 6+__=9.
Answer: 3
03Complete __+4=10.
Answer: 6
04Whole 8, known part 3.
Answer: 5
05Use subtraction for whole 10, part 7.
Answer: 10−7=3
06Check missing part 4 for 5+__=9.
Answer: 5+4=9, so it is correct.
07Why does the missing part matter?
Answer: It completes the known part to make the whole.
08Explain two solution methods.
Answer: Count on/add to the whole, or subtract the known part from the whole.
Terminology
Words to know
- unknown
- A value not yet known.
- missing part
- The unknown part needed to complete a known whole.
- inverse operations
- Operations that undo or reverse each other, such as addition and subtraction.
- verify
- Check that a result satisfies the original relationship.
Continue learning
Connected concepts
Curriculum references
Standards and instructional references
California Common Core State Standards for Mathematics — Kindergarten Operations & Algebraic Thinking
Standards progression for addition/subtraction stories, unknowns, and making ten.