Quick guide to fraction operations: match denominators for add/subtract, multiply straight across, flip for division, then simplify.

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In June 2012, Arto Inkala, a Finnish mathematician, claimed to have make the world's hardest sudoku.

It took him 3 months to design it, and there's only one possible solution.

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If you divide 1 by 998,001 you get all three-digit numbers from 000 to 999 in order, except for 998.

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Each of the white circles are really just moving back and forth along a straight line.

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