Math Encounters -- Secrets of Mental Math 

what is the website

Not only because he is genius, but he is entertaining. He has the passion of math which he loves teaching so he is entertaining on teaching Math.

nerd

All schools should teach this better system, makes you wonder why they keep us stupid

He copies the number in the second column of the first row to the first column of the fourth row. Then, in the box in the second column of the third row, he adds 1 to the number in the third column of the first row. He then has three of the four numbers in the diagonal from bottom left to top right. He knows what the total should be, so can place the missing value in the third column of the second row. He knows that the four numbers in the top right quadrant also add up to the same total, so he can add the missing value to the fourth column of the second row. He knows that the four corners replicate the desired date, going anti-clockwise from the top left, so can add the missing value to the fourth column, fourth row. He now has three numbers in the fourth column, so can add the missing one to the third row. Moving on to the centre top quadrant, he already has three numbers, so can add the missing value to the second column, second row. He can then fill in the missing number in the first column, second row, by adding the second row or the top left quadrant. He can then fill in the number in the third column, third row, as he already has three numbers in the centre quadrant (and also the top left to bottom right diagonal). Then, he's only missing one number from each of three columns, so can add the missing numbers to make the columns add up to the desired total. You can try it yourself -with any date - you only need to remember the first two numbers to add to the square, then you've always got three of the four numbers you need to add one missing digit. You just need to remember that the centre left and centre right quadrants won't add up to the desired total, so don't use these. You just need to hope that your volunteer doesn't have a birthday in January or on the first of the month, otherwise you will have zeroes in the magic square. I'm sure Dr Benjamin has a way to get around this problem, but I'm nowhere near as clever as he is!

Thanh phan tan You don't have to subtract from 4872 because doubling 4872, then subtracting 5000 could give you 4744 much faster than subtracting 128 from 4872 mentally. Since 4872 rounds up to the nearest thousand of 5000 (three zeros), you can make things a little easier by just doubling 872 (last three numbers from 4872) to make 1744. and replace 872 with 744 to get 4744. He explains the same concept at 47:00 but with a 3 digit number. That should make it easier to look at.