A
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B
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A and B
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A or B
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A xor B
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Neither A nor B
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Not A
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Not B
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When trying
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... A always occuring
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... A never occuring
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... B always occuring
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... B never occuring
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Probability Calculator

By and

With the probability calculator you can investigate the relationships of likelihood between two separate events. For example, if the the chances of A happening is 50%, and the same for B, what are the chances of both happening, or only one, or at least one, or neither, and so on.

Below you'll discover:

  • How to use the probability calculator properly
  • How to find probability of single events

How to use the probability calculator

To make the most of our calculator, you'll need to take the following steps:

1. Define the problem you want to solve.

Your problem will need to be condensed into two distinct events. If you want to calculate the probability of an event in an experiment with a number of equally possible trials, you can use the z-score calculator to help you.

2. Find the probability of each event.

The probability of a single event is known as its P-value. You'll find p-value calculator very useful.

3. Type the percentage probability of each event in the corresponding fields.

Once they're in, the probability calculator will immediately populate with the exact likelihood of 6 different scenarios:

  • both events will happen
  • at least one of the events will happen
  • exactly one of the events will happen
  • neither of the events will happen
  • only the first event won't happen
  • only the second event won't happen

The calculator will also show the probability of four more scenarios, given a certain number of trials.

  • A always occurring
  • A never occurring
  • B always occurring
  • B never occurring

How to find probability of events

Again, the probability of a single event is called it's P-value, and you can express it as such:

  • The probability of A = P(A)
  • The probability of B = P(B)

The basic definition of probability is the ratio of the number of a chosen outcome to the total number of all possible outcomes. So, if you want to know the probability of picking a red marble out of a bag of 50 marbles where only 10 are red, the answer will be one in 5, 1/5, or 20%.

We use intuitive calculations of probability all the time. Knowing how to quantify likelihood is essential for statistical analysis. It allows you to measure this otherwise nebulous concept called "probability".

Further reading

If you're interested in applications of the probability theory, make sure to check out the risk calculator and the relative risk calculator.

Mateusz Mucha and James Mathison

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