Probability in percentage terms Is it correct to express probability in percentage terms. For example it is common to read in newspaper reports that there is 80 % probability of rain/monsoon/ etc.
Shouldn't probability be always expressed between 0 - 1 ?
I searched on net but could not find a satisfactory answer.
 A: We used the term "per cent" just as a matter of convenience. Remember that these are just human conventions to help us interpret the data in a way that is most intuitive to us. We can interpret "It has a probability of $ 45.45 \% " $ better than "It has a probability of $0.4545. $". And sure enough, as the other answer points out, $ 45.45 \% $ just means $ \dfrac{45.45}{100} $ which falls in the range $ [0,1] $.
You could even make it per million and multiply the number between $0$ and $1$ by $1,000,000$ to represent probability.
A: "Per cent" means (from Latin) "for every hundred", thus $80$% means $80$ for every $100$. Of course, $80/100$ does fall within $[0,1]$. It's really a matter of choice whether to use percentages or to simply say "the probability is $0.8$", but if you choose the former be sure to say/write "per cent" or the symbol % to express probabilities that way.
Another point is that many probabilities are proportions (the probability of drawing an ace is the proportion of aces in the deck), and so percentages are a natural way to express such probabilities.
