Math Is Fun Forum

John E. Franklin

Member

Registered: 2005-08-29

Posts: 3,588

multiply near the center of 2 numbers

Here's a
peculiar long
way to multiply
2 times 7. (Note that 2 is even and 7 is odd)

2 + 7 = 9
  9 is 4 + 5, the central numbers, close to 9/2.
     Remember the number 4 times 5 = 20, we'll use it soon.

7 - 2 = 5
  5 is 2 + 3, the central numbers close to 5/2. (Don't use 1 + 4)
      Remember that 2 times 3 is 6, we'll use that soon.

Recall the 20 and the 6 above and use it below.

20 - 6 is 14, and that's the answer to 2 times 7 we started with!!!!

Remember when finding the central numbers, they have to
be beside each other or two of the same number.

I'll do another example where the central numbers are the same number.
This happens when the sum and difference of the problem numbers is an even number.

Now we'll do two even numbers.
4 times 10
4 + 10 = 14 and 14 breaks into 7 + 7, so remember 7 times 7 = 49.
10 - 4 = 6 and 6 breaks down into 3 + 3, so remember 3 times 3 = 9.
Now use the remembered numbers.
49 - 9 is 40, that's the answer to 4 times 10 !!!!

Now we'll do two numbers that are the same number.
Two odd numbers.
11 times 11 is the problem this time.
11 + 11 = 22 and 22 breaks down to 11 + 11, so remember 11 times 11 which is 121.
11 - 11 = 0, and 0 breaks down to 0 + 0, so remember 0 times 0 = 0.
Now take the remembered numbers and subtract them.
121 - 0 is 121, and that's the answer to 11 times 11 !!!!  Ha Ha

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igloo myrtilles fourmis

ZHero

Real Member

Registered: 2008-06-08

Posts: 1,889

Re: multiply near the center of 2 numbers

Cool Trick!

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If two or more thoughts intersect, there has to be a point!