Random appears in latex writing

When the following is written in a forum post:
[latex]\frac{1}{20A} + \frac{1}{20(20-A)}[/latex]
This is the output: https://s.wordpress.com/latex.php?latex=%3Cspan%3E%5Cfrac%7B1%7D%7B20A%7D%20%2B%20%5Cfrac%7B1%7D%7B20%2820-A%29%7D&bg=FFFFFF&fg=000000&s=0
How can I ensure that the < span > doesn’t randmomly appear?

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