Grade 1 · Place Value · MAT-01-PV-008
Subtract Multiples of 10
Subtract a multiple of ten from a two-digit number by removing tens.
Learning objectives
What you should be able to do
- Subtract a multiple of ten from a two-digit number by removing tens.
- Explain why the ones digit stays unchanged when only full tens are subtracted.
- Use base-ten blocks, expanded form, and number-chart hops to model the subtraction.
Prerequisite check
Make sure the foundation is ready.
Checks single-ten subtraction.
Checks place-value structure.
Learn
Build the idea from meaning, not memorization.
Subtracting tens removes whole tens
In 76−20, start with 7 tens and 6 ones. Remove 2 tens, leaving 5 tens and 6 ones: 56.
Ones stay unchanged when only tens are removed
Because no ones are subtracted, the ones digit remains the same. 64−30 becomes 34: six tens become three tens, while four ones remain.
Expanded form shows the reasoning
83−40 = (80+3)−40 = 40+3 = 43. Separating place values keeps the operation clear.
Number-chart hops can verify
Each upward row on a ten-column chart subtracts ten. Subtracting 30 is three ten-hops upward.
Interactive math lab
Change it. See what stays true.
Base-Ten Lab
Change hundreds, tens, and ones and watch the total rebuild from place value.
- remove ten rods
- chart ten hops
- expanded form
- cross 100
Worked examples
Twenty different ways to see the concept work.
35−10
25Remove one ten.
47−20
27Remove two tens; 7 ones stay.
58−30
285 tens−3 tens=2 tens.
69−40
296 tens−4 tens=2 tens.
76−20
56Remove two tens.
84−50
348 tens−5 tens=3 tens.
92−60
329 tens−6 tens=3 tens.
99−90
9Nine tens removed; nine ones remain.
70−30
407 tens−3 tens=4 tens.
60−60
0All six tens removed.
83−40 expanded.
(80−40)+3=43Ones unchanged.
54−20 expanded.
(50−20)+4=34Subtract tens.
Which digit stays same in 67−30?
7No ones are subtracted.
67−30
376 tens become 3 tens.
100−20
8010 tens−2 tens=8 tens.
110−30
8011 tens−3 tens=8 tens.
Chart: 3 rows up from 85.
55Each row subtracts ten.
Why is 45−20 not 25 by ones counting?
It is 25, but place-value removal of two tens is more efficientNo need for twenty single steps.
Can 34−50 be solved within current nonnegative Grade 1 range?
Not as a nonnegative whole numberThe subtracted tens exceed the available tens.
Explain 78−40.
7 tens 8 ones minus 4 tens = 3 tens 8 ones =38Only tens change.
Practice
Guided practice with hints
01Solve 64−20.
Hint: Remove two tens.
Answer: 44
02Solve 87−50.
Hint: 8 tens−5 tens.
Answer: 37
03Which digit stays same in 59−30?
Hint: Ones digit.
Answer: 9
04Solve 100−40.
Hint: Ten tens minus four tens.
Answer: 60
05Show 73−20 on a chart.
Hint: Two rows up.
Answer: 53
06Why not change ones?
Hint: No ones were subtracted.
Answer: They remain the same.
Practice
Independent practice
0146−10
Answer: 36
0257−20
Answer: 37
0368−30
Answer: 38
0479−40
Answer: 39
0595−50
Answer: 45
06100−70
Answer: 30
07What usually stays same?
Answer: Ones digit
08What unit is removed?
Answer: Tens
Common mistakes
Learn to catch the error, not just the answer.
Remove tens rods; leave ones untouched.
Use ten-hops or tens blocks.
Check the starting number before removing tens.
Applications & challenge
Use the idea beyond a single exercise.
Applications
- Reduce a two-digit inventory after removing bundles of 10.
- Use chart hops to model decreases by tens.
Challenge problems
Subtract 70 from 98.
28
What is 20 less than 104?
84
Why does the ones digit stay 6 in 86−50=36?
Only five tens are removed; six ones are untouched.
What is 30 less than 72, then 20 less again?
42, then 22.
Flashcards
Retrieve it from memory.
Flashcards
Card 1 of 6
Game mode
Take Away Tens
Remove tens rods or make ten-hops while preserving the ones.
Practice
Mastery check
0163−20
Answer: 43
0288−40
Answer: 48
0395−70
Answer: 25
04100−30
Answer: 70
05Which digit often stays same?
Answer: Ones
06Why?
Answer: Only full tens are removed.
07Show 74−20 in expanded form.
Answer: (70−20)+4=54
08How can a number chart verify?
Answer: Each row up subtracts ten.
Terminology
Words to know
- multiple of ten
- A number made of whole tens, such as 20, 40, or 90.
- ten-hop
- A move of 10 on a number chart or line.
- difference
- The result of subtraction.
- expanded form
- A number written as the sum of place-value parts.
Continue learning
Connected concepts
Curriculum references
Standards and instructional references
California Common Core State Standards for Mathematics — Grade 1 Number & Operations in Base Ten
Grade 1 place-value arithmetic and mental-ten relationships.