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Kangaroo Math

Recently I saw this image (hopefully it comes in). I do not know if this is true or not. The writer/creator has the same thoughts as me. This got me thinking about the number line method displayed. After a little research, I discovered this method is commonly used in some states. Trying to keep my emotions in check I will go over this means of learning.
The method of using a number line as a means of adding and subtracting apparently comes from the Netherlands. This is the one source I found. The method is used as a visual representation for the students thinking strategy.

An empty number line is introduced where students are asked how to get from one number to another in the “least number of jumps of tens and ones.” An example of this would be going from 0 to 69. You would make 7 jumps of ten to 70 and jump back one to 69.

This same application can be used for addition and subtraction. How do you go from 31 to 82 in a small number of jumps? In my example I would “jump” 50 to get 81 and make a short “jump” of 1 to get to 82. Isn’t this so easy and understandable?

Apply it to a word problem. I’ll enlist Jack’s help. A tree in Jack’s yard is 57 cm tall. It grows another 42 cm during the summer. How tall is the tree, Jack? Our friend Jack draws a blank number line and writes 57 on the left. Jack still figuring this new math out does a jump of 40 to get to 97. Not wanting to waste jumps, Jack does a jump of two to get the answer of 99. Good boy Jack. Do you understand now? No?

We will give Jack another problem to help understand. This time it will be a subtraction problem. Ready Jack? Do you like XBox games? Yeah? Alright Jack, here is the problem for you concerning XBox games. Jack wants the latest XBox game. He needs 83 dollars to buy the game. He only has 35 dollars saved. How many more dollars do you need to save Jack? Get that number line drawn! This time Jack writes 35 dollars on the number line. Put it on the left side Jack. Jack wants to do an initial jump of 50 which gives him 85. Now Jack will jump back 2 to get 83. This method of subtraction is using something called friendly jumps. Not sure what that means.

Jack still does understand subtraction. It could be all of the friendliness in the word problem. We will let Jack attempt another subtraction problem. Jack has a board that is 53 cm long. He wants to cut off 26 cm. How will be left. Jack dutifully draws that blank number line. Here is a hint jack. Write 53 on the right side of the number line. I know, I know. It isn’t what you did the last time. Jump away Jack! Jack is making a reverse jump or subtraction of 20 to get 33. Next jack jumps back again 7 to get 26. Good job Jack!
What about three digits? Can you do those Jack? It’s easy with the number line method. What? You still have difficulty knowing what direction to go? We have 443 students taking math. 220 are pulled out of school because of Common Core. How many student remain? We start with 220 on the line. Jump 80 to get 300. Jack does another jump of 100 to get to 400. Now Jack jumps 43. If Jack drew his jumps properly and labeled each jump, he should have the answer by adding the values of the jumps which is 223. Wow!! This is so simple and easy! Had I gone through this as a kid I would be a mathematician. Oh, wait. I am one.

Jack, are you ready for multiplication? No. Too bad. We are going to calculate 18 x 4. Apparently, numbers like 20 are considered friendly. Add 2 to 18 to get our friend, 20. Do 4 jumps of 20 to get 80. Now we have to jump back 4 spaces two times to 72. This is amazing!

Isn’t it nice to know this method of Common Core is so easy to learn.

Categories: Education Tags: , ,
  1. March 26, 2014 at 12:46 am

    I see how they are trying to teach them, but I too think they are using a more complicated method. Perhaps the purpose is to make this easier when doing strictly mental math and not written down?

    • March 26, 2014 at 1:08 am

      You need to understand the concept before mental math can take place. The purpose of this is to show different ways of solving the problem. It fails in the confusion of solving the problem. Another issue for me is the need to write a “letter”. I would use the Saxon Math Manipulation Kit in place of a blank number line.

      • March 26, 2014 at 3:17 pm

        I am by no means defending their theory, but I wonder if they are trying to combine quite a bit into the arithmetic lesson.

        It seems they are trying to not only arrive at the right answer, but have the children understand why, all while demonstrating they can correct someone by appropriate means. A lot is going on in this lesson outside of the arithmetic factor.

        I agree though… their method is very confusing!

      • March 30, 2014 at 11:35 am

        No, I am not saying you are and understand (I hope) your point of view.

        Visual aids such as abacuses or images are far easily to understand. As a child in grade school, I used little blocks to represent the place values. It took little time to understand. Out of twenty-five students, I would say twenty understood while the other five didn’t care. Utilizing numbers line are not necessarily bad. The biggest part of the issue for me was the question.

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