Georgia 1.NR.5.2
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.
Georgia's K-12 Mathematics Standards · Use concrete models, the base ten structure, and properties of operations to add and subtract within 100.
Teacher's field guide
What This Standard Means
What Students Need to Do
- Students add or remove one group of ten from a two-digit number in their heads. They use place value to explain why the ones stay unchanged.
What Mastery Looks Like
- Given 47, a student quickly names 57 and 37 without counting by ones. The student explains that only the number of tens changed.
Common Misconceptions
- Students may change the ones digit instead of the tens digit. Some count by ones, reverse the direction, or struggle when the result reaches 100 or 0.
How to Assess It
- Exit ticket: For 46, write the number after adding one ten and after removing one ten. Explain what changed in each answer.
Lesson moves
Ways to Teach It
Build 34 with base-ten blocks, add or remove one tens rod, and record the new number.
Ask, “Why does the ones digit stay the same when one group of ten is added or removed?”
Students draw two-digit number cards, name the number with one more or fewer ten, and earn a point for a correct explanation.
Use classroom supply boxes holding ten pencils each, then find totals when one full box is added or removed.
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Printable 1.NR.5.2 Worksheet
A ready-to-print activity worksheet aligned to 1.NR.5.2, with an answer key for the teacher on its own page. No account needed.
PDF, US Letter, prints cleanly in black and white.
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Related Standards
- 2.NR.2.2
Find 10 more or 10 less than a given three-digit number and find 100 more or 100 less than a given three-digit number.
- 5.NR.1.1
Explain 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 represents...
- 3.PAR.3.5
Use place value reasoning and properties of operations to multiply one-digit whole numbers by multiples of 10, in the range 10-90.
- K.NR.1.3
Given a number from 1-20, identify the number that is one more or one less.
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