# Bayes Theorem probability

Hello.

I know that total probability formula is in Bayes formula/Theorem. But how do I know when I must use
- total probability formula ?
- Bayes formula?

I want to know what is difference between total probability formula and Bayes formula/Theorem.

I don't know when total probability formula is ( Bayes formula is not needed ) enough?

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chiro
Hello.

I know that total probability formula is in Bayes formula/Theorem. But how do I know when I must use
- total probability formula ?
- Bayes formula?

I want to know what is difference between total probability formula and Bayes formula/Theorem.

I don't know when total probability formula is ( Bayes formula is not needed ) enough?
Hello philipSun and welcome to the forums.

One guiding principle that you should use when solving any problem (especially mathematical, scientific and so on), is to look at the information you are given.

Just list all the information you have in mathematical language and then see if you can transform it to something that you need.

If you are given conditional information, then you might have to use that to get some other probability, or if you are given non-conditional probability, then you might have to use that to get conditional probability and so on.

There is no straight up final answer to your question. Basically a lot of mathematics is about representing the same thing in a few different ways and the probability theorems are no different.

After you do a few problems, you'll pretty much know what you have to find and what kinds of information you are given in terms of probabilities (like P(A|B = 1) = 0.2, P(A and B) = 0.13 and so on).