Standard: 1.NBT.C5 – Given a two-digit number, mentally find 10 more or 10 less than the number, without having to count; explain the reasoning used.
Grade level: Grade 1
Subject: Mathematics
Domain: Number & Operations in Base Ten
Teacher Overview
This standard focuses on developing students’ mental math skills by finding 10 more or 10 less than a given two-digit number. This is important for building number sense and understanding place value, which are foundational for more advanced mathematical concepts. Students should be comfortable with basic counting, understand two-digit numbers, and have a basic grasp of addition and subtraction before tackling this standard.
Mastering this standard will prepare students for more complex mental arithmetic and a deeper understanding of place value, which are crucial for future mathematical learning.
Common Misconception 1
A common misconception is that students feel they need to count each number individually to find 10 more or 10 less. This shows a lack of understanding of place value and number patterns.
Intervention 1
To remediate this, use number lines or base-ten blocks to show how adding or subtracting ten affects the tens place while the ones place remains the same.
Common Misconception 2
Another misconception is confusing adding or subtracting ten with adding or subtracting one, which indicates a misunderstanding of place value.
Intervention 2
Visual aids like number lines or base-ten blocks can help students see the difference between adding/subtracting ten and one, reinforcing the concept of place value.
Prerequisite Knowledge
Students should understand basic counting, be familiar with two-digit numbers, and have a foundational grasp of addition and subtraction.
Subsequent Knowledge
Students will develop skills in more complex mental arithmetic, including addition and subtraction of larger numbers, and an understanding of place value in greater depth.
Instructional Activities
- Using number lines to practice adding and subtracting ten
- Playing games that involve adjusting scores by ten
- Using base-ten blocks to visualize adding and subtracting ten
- Creating story problems that require finding 10 more or 10 less
