A handbook of magical mathematical tricks for you to learn
Do the same thing with the spectator’s number and once you have made the grid hand it back to them. Ask them if they can see where you’ve hidden their original number (in the example it was 201). They will say that they can’t see it anywhere. Then tell them that in fact their number is everywhere in the grid, get them to add the numbers in any row, or in any column or even the diagonals and they will add up to their number! Incredible! Clearly only someone with a truly magical brain could have the mental power to produce this.
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One more tip to help your mental methods; if your numbers have decimals or lots of “0s” at the end you can divide or multiply by 10s and take the 10s out of a bracket to make it easier. e.g. 6000 x 5.32 = (6 x 1000) x (532 / 100) = (6 x 532) x 1000 / 100 = (6 x 532) x 10