Subtraction with Regrouping Number Line: 2-Digit Strategy
Subtraction with regrouping on an open number line is a useful strategy for students to keep track of parts of numbers when subtracting large numbers.
The standard 2.NBT.5 uses many different strategies to master 2-digit addition and subtraction. I take it very slowly to help with mastery of this standard. I give students many chances to find a strategy that works for them before teaching the traditional algorithm.
Keep reading to learn more about the open number line strategy and to find a resource you can use right in your classroom to teach 2-digit subtraction with regrouping using an open number line.
Subtraction with Regrouping Number Line: 2-Digit Strategy Example
What do you think you would do to start solving 63 – 24 using the open number line strategy?
You would start with an open number line, which is just a blank number line. In a subtraction problem, the starting number is the minuend (63 in this example).
Place 63 on the right side of the number line. (This is different from addition, where you start on the left side.)
Many students will want to start drawing tick marks to keep track of numbers, but that ends up being a waste of time.
Once you have your starting number on the number line, you look at the subtrahend to see what jumps of tens and ones you can make.
In this example, I am subtracting 24 from 63.
I start making one jump of ten. When I subtract 10 from 63, the difference is 53.
Note: It is very important that your students write the sum after their jumps as they go. It is easy to make a mistake if you make all the jumps and fill in the sums after.
Since the problem is 63 – 24, I still need one more jump of ten.
Once you finish subtracting all the tens, you are ready to subtract the ones.
You have now made two jumps of ten and four jumps of one.
63 – 24 = 39
To help my students remember to write the sum when they make their jumps, I have them think of an airplane taking off from one airport and landing at another airport that many jumps ahead. They have to know where the airplane lands before it can take off for another airport.
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An open number line can be used in many different ways. The example I showed was just one way to subtract using an open number line.
Your students might be able to make a jump of 20 or 30 instead of jumps of 10.
I make sure students understand jumps of tens and ones before showing them how to make jumps with larger numbers.
An open number line provides many options for differentiation within the same strategy.
Subtraction with Regrouping Number Line: 2-Digit Strategy Practice
Do you need some practice pages for your students to use with this strategy?
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Comment below with any questions you have about the subtraction with regrouping number line strategy I explained today.
