Karen Rainier

Web Drop In #1

June 20, 2009

 

 

 

 

Let’s Explore Subtraction with Virtual Manipulatives!!!!

 

 

ü     In this Math Cluster, we are going to be learning about how to subtract 2 and 3 digit numbers by regrouping.

ü     Regrouping in Subtraction – means taking a ten block, breaking it apart into ten ones, and moving the ones to the ones place.

ü     We have used base ten blocks and other manipulatives in class to help us add, subtract and learn about mathematical concepts.

ü     Now we are going to explore how to use virtual base ten blocks to help us subtract using regrouping.

ü     We will go to the National Library of Virtual Manipulatives to use the virtual base ten blocks to help us subtract.

ü     You will need your math journal to help you tell about what you learned, and your math brain to help you do the learning J

 

Follow the directions below to explore the virtual base ten blocks and use them to solve the subtraction problems.

 

1. First we will explore the manipulatives available to us. Click on the link here: National Library of Virtual Manipulatives

* Look at the list of virtual manipulatives.

* Which ones do you think would be helpful with learning the 2nd grade skills we have learned so far?

* Choose any set of virtual manipulatives, click on it, and explore using it.

* In your math journal, record the problem you solved with the manipulatives. Remember to tell WHAT YOU DID and HOW you solved it.

 

2. Before using the virtual tools, use your most useful tool, your math brain! Think about how you could do the following problem:

 

                                                 42

                                              -  27

 

   * We know we need to start in the ones place and subtract the ones, but how can we subtract 7 ones when we only have 2 ones???

   * In your math journal, record the equation. Write a sentence explaining your math ideas about how you think we could solve this problem.

 

3. Now, we will try using the base ten blocks to explore subtraction with regrouping. Click on the link here: Base Ten Subtraction

* Click on the box that says “Create Problem”.

* At the bottom, there is a box that says “Columns”. We are doing a 2 digit problem, so we only need 2 columns. Click on the down arrow to

                               get 2 columns.

* The blue base ten blocks will show the bigger number, and the red ones will show the smaller number that we will be subtracting.

* Click on the red tens and ones to show the number 27. (2 tens and 7 ones)

* Click on the blue tens and ones to show the number 42. (4 tens and 2 ones)

                             * Now you have your virtual math problem ready!!! Click on the box that says “Begin Problem”.

 

4. It is time to solve and find the difference! First, we need to subtract the ones…but, UH OH…. we don’t have enough!

* What can we do? Let’s take a blue ten and move it over to the ones place.

* Now we have 3 tens left in the tens place and 12 ones in the ones place- Look at the equation- the computer did that part for you! J

* Copy down the computer’s equation on your equation in your journal like this: 

     **Cross out the 4 tens and make it 3 tens, then cross out the 2 ones and make it 12 ones.

* Moving the ten over is called regrouping. Why do you think we did that?

* Write a sentence in your math journal explaining why you think we moved a ten over to help us subtract.

*To subtract the ones, click on a red ones cube. Drag it over a blue ones cube. This will show that you are taking one away.

* Keep doing this until you have taken away all the red ones. How many blue ones are left? Check the computer’s equation for accuracy.

* Record the difference in the ones place in your math journal.

 

5. Now it is time to subtract the tens. Do we have enough?? YES!  So…

*To subtract the tens, click on a red tens cube. Drag it over a blue tens cube. This will show that you are taking a ten away.

* Keep doing this until you have taken away all the red tens. How many blue tens are left? Check the computer’s equation for accuracy.

* Record the difference in the tens place in your math journal.

 

CONGRATULATIONS!!!! YOU SOLVED A SUBTRACTION PROBLEM WITH VIRTUAL MANIPULATIVES!!!

 

6. Now, in your math journal,tell how you solved the problem with regrouping, and how the virtual base ten blocks helped you.

 

 

Would you like to try it again?

You can click the button that says “Create Problem” to make your own subtraction problem

 Or you can click the button that says “New Problem” to let the computer give you a problem to solve.

J HAPPY PROBLEM-SOLVING!! J