Hey teacher friends! When I taught second grade math, I had to learn all the many math strategies and which ones would be the most effective for my students. We all know that all students learn differently. Some strategies work better than others. I’ve had students who love models, but others who dispise them. Some have preferred number lines while some like the to count using mental math strategies. Learning how to subtract can be a mountain for some students and so it’s great to have several options when teaching it.
If your kiddos are subtracting numbers within 100, here are several strategies you can use to make the process easier and more efficient. Here are some common strategies:
Counting
1. Counting Backward: Start with the larger number and count backward by ones until you reach the smaller number. For example, to subtract 47 from 83, start with 83 and count backward: 82, 81, 80, 79, 78, 77, 76, 75, 74, 73, 72, 71, 70, 69, 68, 67. Counting backward can be done mentally or by using your fingers or number line.
Breaking the Numbers Apart
2. Decomposition: Break down the numbers into smaller components to simplify the subtraction. For example, to subtract 47 from 83, you can break down 83 as 80 + 3 and subtract 47 from each part separately: 80 – 40 = 40 and 3 – 7 = -4. Then, combine the results: 40 – 4 = 36.
Numberlines
3. Using Number Lines: Draw a number line and mark the starting number and the number to subtract. Then, count backward on the number line to find the difference. This strategy provides a visual representation of the subtraction process and helps with understanding the relationship between numbers.
Multiples of 10
4. Compensation: Try to find multiples of ten. If the number being subtracted is close to a multiple of 10, you can adjust the subtraction to make it easier. For example, to subtract 47 from 60, you can compensate by subtracting 50 from 60 and then subtracting the remaining 3: 60 – 50 = 10 and 10 – 3 = 7.
Place Value
5. Using Place Value: This is one of my personal faves. Here’s how you do it! Subtract the digits in each place value column separately, starting from the rightmost column and moving to the left. Borrowing may be necessary when subtracting across place values. For example, to subtract 47 from 83, subtract the ones place digits (3 – 7 = -4), then subtract the tens place digits (8 – 4 = 4), resulting in 36.
Mental Math
6. Mental Math: Lastly, if the numbers are small and can be easily solved mentally, you can simply subtract them mentally. Some students prefer mental math especially if they know their mat facts very well. This strategy is awesome with practice and more number sense development overtime.
Remember, the most effective strategy depends on the specific numbers involved in the subtraction problem. Practice using these strategies with your kiddos, and choose the one that works best for you students.
