How do you calculate probability

Question

How do you calculate probability?

How can you connect probability to the really world

Answer 1

Basically, you observe processes and apply reasoning + the relevant physics. Consider the most basic example: A perfectly symmetrical and balanced disk (e.g. a coin) has no preferred way of landing. We can use logic + physics to predict that the probability of landing on side A is the same as for side B. We can then test this using observations.

Another basic example is picking a marble out of a container. If there are 100 marbles total, and 30 are red---and they are all the same size and weight---then the probability of selecting a red one (blindfolded) is 30/100 = 0.3. In this case, there is no physics involved---the probability is solely based on the number and features of the objects.

Probability and statistics also includes the art and practice of "good enough". Going back to the coin, we could easily have one that is out of balance and might consistently come up heads 503 times out of 1,000. This is a probability of 0.503, but we might still use 1/2 (0.500) simply because that is good enough for the problem at hand.

Answer 2

Coin; 5 tosses=1 tail?

=1-p(0 tales)=1-(.5)^5=.96875

Answer 3

Wyzant lost my original answer to your question, but your question demands that I try to re-write it.

You need to do some reading. The very superficial questions you have asked make clear that you have little understanding of mathematics, probability theory in particular. Probability theory is a very profound area of mathematics with far reaching implications.

Probability as a general concept should be thought of as a function which maps a sample space onto the closed real interval from 0 to 1. In a discrete sample space, probability is the ratio of the number of elements in a particular subset of the sample space to the number of elements in the entire sample space, e.g. 36 points in the throw of 2 dice.

In a continuous sample space the idea is similar but involves the measure of the subset to the measure of the sample space. This theory involves some of the most abstruse and difficult ideas in all of mathematics.

Probability theory is involved in all sorts of "real world" ideas from particle physics to experimental statistics to gaming theory. To go back to my original point: you need to do some reading and learning to cure your ignorance before you ask such a superficial question!