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Please can someone explain to me how this probability equation evaluates to 0.5

[tex]\frac{2^{f(n)+2}}{2^{f(n)+1}} = \frac{1}{2}[/tex]

f(n) is essentially anything in this context.

For me the probability evaluates to 2, but this is straight out a research paper and I cant doubt their maths.

This is the context:

Because there are [tex]2^{f(n)+2}[/tex] texts with length [tex]f(n)+2[/tex], the probability for a selected text with length [tex]f(n)+2[/tex] having a related

compressed text of length ≤ f(n) is less than [tex]\frac{2^{f(n)+2}}{2^{f(n)+1}} = \frac{1}{2}[/tex]

Please can someone explain to me where the 0.5 comes from? I can see if i turn the equation upside down it works, but Im guessing its not that simple :p

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# Simple Probability Equation

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