1st Grade · Math · Parent guide
Subtracting Tens From Tens, 10 Through 901.NBT.C.6
Short answer. First graders subtract tens from tens, like 70 - 30, using place value thinking. What the standard means plus easy practice with dimes and snack bags.
- Grade
- 1st Grade Learning level
- Subject
- Math Skill area
- Framework
- Common Core State standards guide
Quick answer
What 1.NBT.C.6 means in plain English
Your child subtracts round numbers from round numbers: 70 - 30, 90 - 40, 50 - 50, always multiples of 10 between 10 and 90, never dipping below zero. The point is not the answer so much as the thinking: 7 tens take away 3 tens leaves 4 tens, shown with objects or drawings, and explained out loud or in writing. They may also use addition to get there, thinking 30 plus what makes 70.
Why parents see this skill
Why this matters
This is subtraction moving up a size class. A child who sees 70 - 30 as tens-minus-tens, rather than a scary big-number problem, has generalized what subtraction means. That reframing carries directly into second grade, where they subtract any two-digit numbers, and into mental math for life.
For reference
The official wording
CCSS.MATH.CONTENT.1.NBT.C.6Subtract multiples of 10 in the range 10-90 from multiples of 10 in the range 10-90 (positive or zero differences), using concrete models or drawings and strategies based on place value, properties of operations, and/or the relationship between addition and subtraction; relate the strategy to a written method and explain the reasoning used.Official Common Core source
See it, then try it
How this skill can look at home
You do not need a lesson plan. Look for these signs in ordinary play, reading, and conversation, then choose one short activity.
What you may notice
- Your child can solve 80 - 50 without counting backward by ones.
- They can show a problem like 60 - 20 with stacks of objects grouped in tens.
- They can explain the shortcut: 6 tens minus 2 tens is 4 tens, so 40.
- They connect it to addition, answering 90 - 60 by thinking 60 + 30 = 90.
- They notice the small-number echo: if they know 7 - 3, they know 70 - 30.
Simple ways to practice
- 01
Dime Heist
Give your child a stack of dimes worth a round amount, say 80 cents. You play the sneaky raccoon who takes 3 dimes. How much is left? Have them answer before recounting, then count to check. Swap roles so they get to be the raccoon.
- 02
Snack Bag Takeaway
Use the bags of 10 from your place value practice (10 crackers or pasta pieces per bag). Lay out 7 bags, so 70. Remove 2 bags and ask what is left. Then write the matching equation together: 70 - 20 = 50. Seeing whole bags leave makes the tens-minus-tens idea concrete.
- 03
The Echo Game
Say a small subtraction fact your child knows cold, like 9 - 4. Then immediately ask its big echo, 90 - 40. Alternate a few pairs: 6 - 2 then 60 - 20, 8 - 5 then 80 - 50. When they start grinning because it is too easy, the standard has done its job.
Choose what helps today
Related guides, activities, and practice
Start with the domain guide for context, use the learning library when a concept needs explaining, or print a page when your child is ready to practice.
- Parent guide1.NBT parent guide
See every 1.NBT skill in order and how the codes fit together.
Open resource - Printable practice1st grade math worksheets
Filter free pages by the exact math skill your child is practicing.
Open resource - Learning libraryNumber learning library
Explore number meaning, formation, examples, and printable practice.
Open resource - Activity setEarly Math Essentials
A short sequence of related early-math pages for repeated practice.
Open resource - Read nextNumbers and counting articles
Parent-friendly ideas for practicing early math in everyday routines.
Open resource
Frequently asked questions
Why does the standard stop at multiples of 10? When do kids subtract numbers like 74 - 38?
First grade deliberately keeps subtraction within 100 to the clean cases so kids can focus on the place value idea without borrowing getting in the way. General two-digit subtraction, including problems like 74 - 38, arrives in second grade. If your child is hungry for more now, mixed problems like 76 - 30 are a reasonable stretch, but they are beyond what school expects.
My daughter counts backward by ones from 70 to solve 70 - 30. Should I stop her?
Do not stop her mid-problem, but do show her the faster road afterward. Lay out 7 stacks of 10 and physically remove 3 stacks, then ask which way felt easier. Counting back 30 ones is slow and error-prone, which kids discover on their own once they have a better option. The standard wants strategies based on tens, and the objects usually sell that idea better than we can.
Keep the sequence
More standards in 1.NBT
- 1.NBT.A.1Count to 120 From Any Starting Number (1.NBT.A.1)
- 1.NBT.B.2Understanding Tens and Ones in Two-Digit Numbers (1.NBT.B.2)
- 1.NBT.B.3Comparing Two-Digit Numbers With >, =, and < (1.NBT.B.3)
- 1.NBT.C.4Adding Within 100 Using Place Value (1.NBT.C.4)
- 1.NBT.C.5Finding 10 More or 10 Less in Your Head (1.NBT.C.5)
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