NC.1.NBT.5
Given a two-digit number, mentally find 10 more or 10 less than the number, without having to count; explain the reasoning used.
Embedded Files
Step 1: Lesson Standards & Learning Goals
This standard focuses on first grade students decomposing a two-digit number into tens and ones and then adjusting the number of 10s by either adding or subtracting one from the tens digit. For example, when asked to find 10 less than the number 52 students should get the number 42 in one of two ways. 1. Students may decompose 52 into 50 + 2 and change the 50 to 40 by subtracting 10 which would get the answer 42, or 2. Students may realize that 52 is 5 tens and 2 ones and realize that 10 less means that the 5 becomes a 4 resulting in 4 tens and 2 ones which is 42.
While this standard calls for students to mentally find 10 more or 10 less than a two-digit number, this work should begin with NC.1.NBT.2 by providing ample opportunities for students to build two-digit numbers and then find 10 more and 10 less than a given number when they have access to ten frame cards, place value (base ten) blocks, or a hundreds board. These visuals will let students move beyond counting on or back by 1s and support their progress towards being able to find 10 more or 10 less mentally. After providing the answer students should be asked to explain how they got their answer. In first grade students may orally explain their thinking, or show their thinking with concrete models, pictures, or equations.
Sample Essential Questions
Sample Essential Questions
How can I find 10 more or less than a two digit number without counting and explain my reasoning?
Why is it important to understand the relationship between the value of a digit and its position within a number?
How does recognizing patterns in place value help us in understanding and working with numbers?
Vocabulary
Vocabulary
adding
decomposing
fewer
less
more
ones
subtracting
tens
Students will be able to...
Students will be able to...
Utilize a variety of strategies to mentally add or subtract 10.
Calculate, using mental math, 10 more from a given number or 10 less from a given number.
Explain or show their thinking for adding and subtracting with concrete models, pictures, or equations.
Students will know...
Students will know...
Mentally adding and subtracting by ten is part of a naturally occuring pattern in the number system.
The concept of place value is significant in understanding numbers.
A digit in one place represents ten times what it represents in the place to its right.
Strategies for identifying the value of a digit in a given number.
Place value understanding is essential when adding or subtracting multi-digit numbers.
The importance of mastering place value in developing overall mathematical fluency and problem-solving skills.
Step 2: Assessment
NCDPI Math Assessment Released Forms
Grade 1 Math Assessment Practice Prompts
Grade 1 Released Summative Assessments
Tools 4 NC Teachers
Tools 4 NC Teachers
Step 3: Lesson Instructions
Possible Activating Strategies
Possible Activating Strategies
Give students a number card with a two-digit number. Pose the question - How do I find 10 more than _______? How do I find 10 less than ________?
Think Pair Share
Pose questions about patterns on the 100 chart. What do you notice?
Video Clip
Teacher Resources
Teacher Resources
Tools 4 NC Teachers
Cluster 5 Lessons
Math Expressions - (Barnes and Hearne) - Standards Alignment
Motivation Math
Think Up! Math
Khan Academy - 1st Grade Math
Eureka Math/Engage NY Free Resources
Topic A: Tens and Ones
Topic B: Numbers to 120
Zearn Math - Online Support Practice for Eureka Math (Requires free account)
North Carolina Collaborative for Mathematics Learning - Grade 1 Instructional Framework
NCDPI Resources
Grade 1 Math Assessment Practice Prompts
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