Subtracting 2 and 3-digit numbers in grades 2 and 3 takes time for many students to master, especially when regrouping is required. Establishing a good understanding of place value is necessary before moving on to operations. Base 10 blocks are great for understanding place value and for simulating subtraction. Representing numbers with base 10 blocks allows students to see the relationship between numbers and the place value system, therefore, they can be an effective manipulative for learning regrouping or borrowing in addition and subtraction. Find the representing and adding numbers post here.
Some of the difficulties that students encounter when solving multi-digit subtraction problems include:
- Difficulty understanding place value: Understanding the value of each digit in a number is essential for solving multi-digit subtraction problems. If a student does not understand the concept of place value, they may have difficulty determining which digits to subtract from which.
- Difficulty with regrouping or borrowing: Regrouping or borrowing is a crucial step in solving multi-digit subtraction problems. If a student struggles with this concept, they may have difficulty determining when to borrow and may not know how to carry out this process correctly.
- Difficulty with subtraction facts: Basic subtraction facts, such as 9-3=6, are essential for solving multi-digit subtraction problems. If a student struggles with these facts, they may have difficulty solving multi-digit subtraction problems, even if they understand place value and regrouping.
- Difficulty with mental math: Multi-digit subtraction requires students to perform complex calculations in their heads. If a student struggles with mental math, they may have difficulty solving multi-digit subtraction problems.
- Difficulty with problem-solving: Multi-digit subtraction requires students to analyze a problem and determine the best course of action to solve it. If a student struggles with problem-solving, they may have difficulty understanding the steps involved in solving a multi-digit subtraction problem.
Teachers and parents can support students by providing them with a variety of strategies and tools to help them overcome these difficulties. Practice with manipulatives and visual models can help students to build their understanding of place value, regrouping, and mental math.
Base ten blocks
I always start with base 10 blocks and make sure that the students are able to represent 2-digit numbers in grade 2 and 3-digit numbers in grade 3. Then we move on to addition and later on to subtraction. I start with subtraction without regrouping and move on to subtraction with regrouping. I prefer to start with the expressions written horizontally 45-26 first. The truth is that we spend a lot of time, solving problems with base 10 blocks and with beads on strings in grade 2, however, I make sure that the students use more manipulatives and more strategies to solve subtraction problems.
100 grids
Another great way to help students represent and subtract 2 and 3- digit numbers are 100 grids. They can see/color the number on the grid and mark the tiles subtracted tens and ones. You can use multiple grids for 3-digit numbers.
100 charts
With grade 2 students you can use 100 charts for the subtraction of 2-digit numbers. The 100 chart works like a number line and allows the students to subtract tens and ones.
Number lines
Never underestimate the power of number lines. I use number lines in different forms for subtracting 2 and 3-digit numbers: Number lines with numbers that look a bit like the 100 chart strategy above, and my favorite, number lines without numbers. Empty number lines allow the students to subtract ones, tens, and hundreds and write the new numbers each time. They can also subtract different convenient numbers.
Expanded Form
When teaching subtraction of numbers vertically/stacked, I always start with the expanded form of the numbers. This is another between-step that helps students remember the value of the digits and helps them understand regrouping much better.
Mental Math Strategies
And last but not least, Mental math strategies. I believe that it is important that we teach our students mental math strategies for solving subtraction problems as well. We need to encourage them to look for relations in numbers that help them solve the problem mentally. I find that sometimes we spend so much time teaching the algorithm that the students forget about other ways of solving subtraction problems. When given a subtraction problem many students rush to stack the numbers and solve it using the algorithm when it can be solved mentally in different ways. Being able to see relations in numbers and use different strategies is what makes our students flexible mathematicians and what makes math fun.
Strategies like subtracting 9, 19, 29, compensating, and balancing are great ways to solve subtraction problems.
Below are some examples
Compensating 75-49=75-50+1=26 199-85=200-85-1=114
Compensating minuend 89-45=90-45-1=44
Decomposing to convenient numbers 67-39=67-37-2=28 443-128=443-123-5=320-5=315
Balancing 392-147=390-145=245 523-318=520-315
I have created two separate collections of slides and print cards with the steps mentioned above to practice subtraction for 2-digit and 3-digit numbers.
Subtracting 2-digit numbers print cards and digital
90 print activity cards and 90 google slides
- Subtracting with base 10 blocks with and without regrouping (the google slides allow to cover and place blocks for regrouping)
- Subtracting using 100 grids (place 10s and ones on the google slides)
- Subtracting using 100 charts
- Subtracting using number lines (numbered and blanc)
- Subtracting using an extended form of numbers
- Subtracting stacked numbers, self-correcting by finding the answer on the card.
- Mental math strategies for subtraction
Google slides Print task cards Bundle
Subtracting 3-digit numbers, print, and digital task cards
80 print activity cards and 80 google slides
- Subtracting with base 10 blocks with and without regrouping (the google slides allow to cover and place blocks for regrouping)
- Subtracting using 100 grids (place 10s and ones on the google slides)
- Subtracting using number lines (numbered and blanc)
- Subtracting using an extended form of numbers
- Subtracting stacked numbers, self-correcting by finding the answer on the card.
- Mental math strategies for subtraction