CCSS.Math.Content.1.NBT.C.5
The Standard
Given a two-digit number, mentally find 10 more or 10 less than the number, without having to count; explain the reasoning used.
Common Core State Standards for Mathematics · Number and Operations in Base Ten
Teacher's field guide
What This Standard Means
What Students Need to Do
- Students mentally find the number that is 10 more or 10 less than a given two-digit number. They explain that the tens digit changes while the ones digit stays the same.
What Mastery Looks Like
- A student quickly states that 10 more than 36 is 46 and 10 less is 26. They explain that the tens digit changes by one while the ones digit stays the same.
Common Misconceptions
- Students may change the ones digit instead of the tens digit, or count forward and backward by ones. They may also reverse the direction and give 10 less when asked for 10 more.
How to Assess It
- Give the exit ticket: “For 47, write 10 more and 10 less. Explain what changed and what stayed the same.”
Lesson moves
Ways to Teach It
Build 34 with base-ten blocks, then add or remove one ten and record the new number.
Ask, “Why does the ones digit stay the same when we find 10 more or 10 less?”
Play a number-card game where partners draw a two-digit number and race to write 10 more and 10 less.
Use classroom attendance numbers and ask how many students there would be with 10 more or 10 fewer children.
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Printable 1.NBT.C.5 Worksheet
A ready-to-print activity worksheet aligned to CCSS.Math.Content.1.NBT.C.5, with an answer key for the teacher on its own page. No account needed.
PDF, US Letter, prints cleanly in black and white.
Download the worksheetLearning progression
Where This Standard Sits
See the whole path on the Number & Operations in Base Ten progression map.
Before This Standard
If students are struggling here, check these first.
- CCSS.Math.Content.1.NBT.B.2
Understanding tens and ones lets students change the tens digit by one while keeping the ones digit the same.
- CCSS.Math.Content.1.NBT.A.1
Reading two-digit numerals and knowing the number sequence supports seeing how numbers change when adding or subtracting ten.
- CCSS.Math.Content.K.CC.A.1
Counting to 100 and by tens supports knowing the decade sequence needed to see 10 more or 10 less mentally.
What This Unlocks
Mastery here sets students up for these next.
- CCSS.Math.Content.2.NBT.B.8
Students extend changing the tens digit by 10 to three-digit numbers and add changing the hundreds digit by 100.
- CCSS.Math.Content.1.NBT.C.4
Mentally changing a number by ten supports adding multiples of ten and tracking tens while ones stay the same.
- CCSS.Math.Content.1.NBT.C.6
Finding 10 less mentally supports seeing each ten subtracted as one fewer ten, but full multiple-of-10 subtraction can use models.
Keep exploring
Related Standards
- CCSS.Math.Content.K.OA.A.4
For any number from 1 to 9, find the number that makes 10 when added to the given number, e.g., by using objects or drawings, and record the answer with a drawi...
- CCSS.Math.Content.5.NBT.A.1
Recognize that in a multi-digit number, a digit in one place represents 10 times as much as it represents in the place to its right and 1/10 of what it represen...
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