# How do I use a:b ?

1. Nov 15, 2006

### quasar987

It has something to do about proportion and fractions. But say I want to express in that notation the fact that some event happens with a probability 2/3. Does that write 2:3 or 2:1 or something else?

2. Nov 15, 2006

### HallsofIvy

Staff Emeritus
A probability is not directly a proportion. If you are talking about the "proportion of 'successes' to all events", then probability 2/3 is 2:3. But if your proportion is "proportion of 'successes' to 'failures'" then the proportion is 2:1 (odds in favor). You could also say, by the way, that the "odds against" are 1:2.