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|
 | Ask a friend to draw a 3x3 box around ANY nine
of the numbers on the calendar.
| Almost immediately you can say what the nine
numbers all add up to!
| See how long it takes your friend to check the
answer on a calculator. (Yawn...snore...zzzz...) | |
For instance, let's say the red numbers are chosen.
. . 1 2 3 4 5
They add up to 198.
THE SECRET: All you do is look at the number in the middle and multiply it by 9.
In this case the middle number is 22 and 22 x 9 = 198.
HANDY TIP: To multiply by 9 quickly, just multiply
by 10 then subtract your number.
So to get 22 x 9 you multiply 22 x 10 =220 (easy!) and then subtract 22. With a
bit of practise you can do this quickly in your head.
| Ask a friend to draw a 5x4 box around ANY
twenty of the numbers on the calendar.
| Almost immediately you can say what all twenty
numbers add up to! | |
For instance, let's say the yellow numbers are chosen.
. 1 2 3 4 5 6
They add up to 290.
THE SECRET: Add together the smallest and the largest numbers in the group. Multiply the answer by 10.
In this case the smallest number is 2 and the largest is 27, so 2 + 27 = 29. Then 29 x 10 = 290.
With the "20 number trick" if the calendar month is February occasionally it will not be possible to put a box round 20 numbers.
These tricks work with ANY grid of numbered boxes, just as long as the numbers are continuous. Try them both on this grid:
13 14 15 16 17 18 19 20 21 22 23Based on Gauss (Nothing to do with Gauss rifles)
's theroy 
The Calendar Trick
