Member #656192

Member Since: March 2, 2015

Country: United States

  • I know I'm a bit late to the discussion, but there's a trick to the division-by-7 thing, too.

    It requires that you memorize 1/7th as a decimal, which is 0.142857 (repeating all six post-decimal digits). Do integer division, then the decimal fraction is always the rotating sequence of those digits, starting with the n-th largest of the digits, where "n" is the integer remainder. So R1 is +0.142857, R2 is +0.285714, R3 is +0.428571, R4 is +0.571428, R5 is +0.714285, R6 is +0.857142. So as long as you can remember the set {1,4,2,8,5,7} and can non-destructively re-sort the set into ascending order, you can divide by 7.

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