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Seven is a number that does not get a lot of respect and maybe it is deserved. It is a serious number. It is hard to see if a number is divisible by 7. It is hard to add seven to a number. And the seven times table is, fof many, one of the last to be automatic with. For example: what is 8 x 7 = ?, well of course you now know it's 56. Until someone told me to reorganize the question visually I had to do 7 x 7 = 49 and then add 7 to get 56. By reorganizing the question, it becomes ? = 7 x 8. Then fill in the numbers. And so, in numerical order 56 = 7 x 8.

Here's another serious seven.

• Choose a number between 1 and 700.
• Divide the number by 7. (you may use a calculator, but it is good practice to do it naturally).
• If you choose a number that was divisible evenly by 7, you either choose a mall number or were lucky. Pick another number and continue.
• Discard the whole number portion of the answer and add up the first six digits after the decimal.
• What's your total?

• Yes, it is 27! Does it happen every time? This is serious!

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Mastering Math Magically
Roger Moore rmoore@telusplanet.net
 last modified: Jan 02, 2000
URL: http://www.telusplanet.net/public/swoitte/Serious Sevens.html