100 using Four 9s

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Puzzle

It is required to express $100$ by four $9$s.


Solution 1

$100 = 99 \frac 9 9$


Solution 2

$100 = \paren {9 + .\dot 9} \paren {9 + .\dot 9}$

where $.\dot 9$ is interpreted to mean point $9$ recurring:

$.\dot 9 := .9999 \ldots = 1$


Sources