Thursday, 20 February 2014

89 and 98

Sometimes the kids come up with some amazing things.

This happened a few days ago.

A young boy was working on activity to do with the Commutative Law. The example we were using involved the sum:

57 + 32 = 32 + 57

In the process of this investigation, the student started to play with the numbers.

"Hey," he said, "Have you noticed that any two numbers that add up to 89, like 57 and 32, can be reversed and the new answer is always 98?"


Try it.

57 + 32 = 89
75 + 23 = 98

61 + 28 = 89
16 + 82 = 98

25 + 64 = 89
52 + 46 = 98


He was right. Having played around with these numbers, I've got an idea about why this happens.

But to get this young boy thinking, I've asked him to look at other 2-digit numbers that end in 9, and three-digit numbers, and is there a pattern, and....

1 comment:

  1. Mr. Ferrington,
    It's Sarah in Alabama again. It's great to see that your students are thinking creatively in your lessons. I'm sure you love your job on those days! I have another question for you. It goes back to last week when you responded that you do not use textbooks in your teaching. In my EDM class this week, I has to write a blog post about the Khan Academy, and I was wondering do you use the Khan Academy in your classroom? If so, how?

    Sarah Richerson
    University of South Alabama
    Mobile, AL, USA


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