Problem: The Digital Century

\[1\;\square\; 2\;\square\; 3\;\square\; 4\;\square\; 5\;\square\; 6\;\square\; 7\;\square\; 8\;\square \;9 = 100.\]

It is required to place arithmetical signs between the nine figures so that they shall equal $100.$ Of course, you must not alter the present numerical arrangement of the figures. Can you give a correct solution that employs 1. the fewest possible signs, and 1. the fewest possible separate strokes or dots of the pen?

That is, it is necessary to use as few signs as possible, and those signs should be of the simplest form. The signs of addition and multiplication ($+$ and $\times$) will thus count as two strokes, the sign of subtraction ($-$) as one stroke, the sign of division ($\div $) as three, and so on.

Solutions: 1

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Project Gutenberg

  1. Dudeney, H. E.: "Amusements in Mathematics", The Authors' Club, 1917

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