_Rule._--Multiply half the sum of the extremes by the square root of
the greatest extreme.
Referring to the example given above, we see that the extremes 1 and
25 added equal 26--half of which is 13; this multiplied by 5 (the
square root of 25) gives 65 as the total for each row.
Again, in the next question, the two extremes 1 and 81 equal 82, half
of this sum is 41, which multiplied by 9 (the square root of 81)
gives 369 as the total for each row.
42. Arrange the figures from 1 to 81 in a square that when added up
horizontally, vertically, or diagonally the sum will be 369.