Ok, im taking a stats course right now and im trying to understand exactly how probability is defined. It says in the textbook that there are a few ways it can be defined. I understand the first one: Assume an experiment with n possible outcomes, each equally likely. If some event is satisfied by m of the n, then the probability of that event is m/n. However, if the events are not all equally likely, then this definition can't be used. There's also the other definitions like empirical probability and subjective probability, but these don't really give you a precise answer. Then there's the axiomatic probability with 4 axioms. But all it says is(adsbygoogle = window.adsbygoogle || []).push({});

1. P(A) >= 0,

2. P(S) = 1,

3. P(A U B) = P(A) + P(B) for mutually exclusive events A and B

4. P(the union of all mutually exclusive events) = sum from 1 to infinity (P(Ai))

this still doesnt give an explicit answer for what the probability of any event A would be! Using 3, to know P(A) i would need to know P(A U B) and P(B), and to know either of those i would need to know the other probabilities.

I think the best definition is the first definition, but then there must be a way to reduce all elements of a sample space to being equally likely.

Any insight would be greatly appreciated.

**Physics Forums - The Fusion of Science and Community**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Probabilty and sample spaces Definition

Loading...

Similar Threads - Probabilty sample spaces | Date |
---|---|

I Standard Deviation Versus Sample Size & T-Distribution | Dec 20, 2017 |

"Probabilty amplitude" meaning ? | Oct 11, 2014 |

Question about normal distribution in probabilty | Jan 12, 2014 |

Correlation and condjtional probabilty | Jul 15, 2013 |

On concave functions over spaces of probabilty distributions | May 9, 2012 |

**Physics Forums - The Fusion of Science and Community**