Quote:
Originally Posted by kstarnes
Those are cool, Rob, and it looks like most of them are actually true - contrary to most of the stuff that gets sent around on the intertubes these days. Thanks! 
This one is really cool:
111,111,111 x 111,111,111 = 12,345,678,987,654,321
Math can be trippy, indeed.
Best,
Kurt |
That formula (tricks/shortcuts of 1's) was taught in elementary:
11 * 11 = 121
111* 111 = 12321
1111*1111 = 1234321
The formula would be (if I recall correctly):
1. drop the last digit of the 2nd number (multiplier or vv?)
2. Using the multiplicand (or vv), start counting sequentially incrementally (left to right) until you run out of digits.
3. Using the multiplier, start counting sequentially from right to left until you run out of digits.
4. Combine the 2 and 3 together.
For example:
One hundred eleven times one hundred eleven
1 1 1 x 1 1 1
becomes:
1 1 1 x 1 1 (drop the last digit)
Count up (left to right) Count up (right to left)
1 2 3 x 2 1
Combine:
1 2 3 2 1 = 12321
Another:
One thousand one hundred eleven times one thousand one hundred eleven
1 1 1 1 x 1 1 1 1
becomes:
1 1 1 1 x 1 1 1
Assigned position value by counting up then down
1 2 3 4 x 3 2 1
Combine:
1 2 3 4 3 2 1 = 1234321
My own translation:
1111 * 1111 = ?
1. You have 2 numbers: they each have 4 digits
2. you actually have 2 numbers: 1 number has 4 digits and 1 has 3 digits.
3. To determine the product: 4 digits and 3 digits is equal to counting 4 times up and 3 times down; so it is 1234321.
Hope this makes sense.