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Calculator Tricks 4 By Brian Carruthers (Please see notes on slide 1)

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Presentation on theme: "Calculator Tricks 4 By Brian Carruthers (Please see notes on slide 1)"— Presentation transcript:

1 Calculator Tricks 4 By Brian Carruthers (Please see notes on slide 1)

2 Lucky 7 or Unlucky 13

3 Step One Think of a three-digit number Enter it twice on your calculator. For example: 123123 Now concentrate on the display.

4 Step Two I think that your number is divisible by 11. Do you believe me? If you don’t then I’ll prove it to you.

5 Use your calculator to check that your number is divisible by 11. Am I right?

6 Step Three But, guess what: Your answer displayed on your calculator is divisible by 13. Again, use your calculator to check the answer.

7 Now, divide your result by your original three-digit number. Your final answer will be : 7

8 Watch this: Enter your original three-digit number twice on your calculator. Divide that number by 11. Now divide your result by 7. Divide your answer by your original three digit number.

9 The answer will be 13

10 Why does this work? Entering a three-digit number twice For example: 123123 is the same as multiplying it by 1001. 123 x 1001 = 123,123. Because 1001 = 7 x 11 x 13, the six-digit number will be divisible by 7, 11, 13, and your original three- digit number.

11 Watch this: 345345 divided by 11 = 31395 31395 divided by 13 = 2415 2415 divided by 345 = 7 678678 divided by 11 = 61698 61698 divided by 7 = 8814 8814 divided by 678 = 13.

12 Now what did you think of that?


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