Why, when the chances of a certain event are 1/10, it's read as the probability is ten to one and not "the probability is one to ten"? Like there's a 10/1 probability of occurrence, which is not possible, since it's limited within 0~1 range. The way it's written in arithmetic notation is pretty straightforward, reading it backwards doesn't make sense to me. How did it come to be like that?


2 Answers 2


I can only speak as it is in Britain, but very often people will say there 'is one chance in ten' of a hurricane.

However, sometimes people will say the odds are 10 to 1. When they do the latter they should say 'the odds are ten to one against'.

If it's the other way around and there is ten times more likelihood of something happening than not happening the expression is 'the odds are ten to one, on', or 'ten to one in favour'.

The betting industry also uses this convention.


It could be one to ten in my opinion.

Its if you mention the event, then its chance to occur goes first, and the chance its against goes second.

so if its a 10% chance that it rains you say:

There's a 9-1 chance that it rains

Theres 1-9 chance that it doesn't rain.

  • 1
    If there's a 10% chance that it rains, I say "there's a nine to one chance that it doesn't rain". Feb 9, 2014 at 15:57
  • Yeah you're right I got it backwards haha
    – Antecedent
    Feb 9, 2014 at 16:10

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