How to find the probability of a simple event happening

Probability 5 Comments

Probability questions are normally word problems that can all be broken down into a few simple steps. This article will tell you how to find the probability of a simple event happening.

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Sample problem: “50% of the families in the US had no children living at home.   22% had one child. 22% had two children. 4% had three children. 2% had four or more children. If a family is selected at random, what is the probability that the family will have three or more children?”

  • Step 1: Identify the individual probabilities and change them to decimals.
    4% of families have two children, and 2% have four or more children. Our individual probabilities are .04 and .02.
  • Step 2: Add the probabilities together.
    .04 + .02 = .06. You’re done!

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  1. How to find the probability of an event NOT happening
  2. How to find the Probability of an Event, Given Another Event
  3. Finding the Probability of a Random Event Probability
  4. How to find the probability of selecting a person from a group or committee
  5. How to find a probability using a standard normal distribution
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5 Responses to “How to find the probability of a simple event happening”

  1. How to Do Everything Statistics » How to find the probability of an event NOT happening said:

    Aug 23, 09 at 8:10 am

    [...] you how to find the probability of a simple event not happening. (You might also be interested in: Finding the probability of an event occurring. How to  find the probability of an event not happening using frequency [...]

  2. Evelyn Snyder said:

    Sep 12, 09 at 8:33 am

    I understand step one, but where does the number 24 come from in step 2?

  3. Stephanie said:

    Sep 13, 09 at 5:07 am

    Evelyn,
    There were two different examples, which was confusing. I changed the numbers, so hopefully it’s more understandable now. Thanks,
    Stephanie

  4. Evelyn Snyder said:

    Sep 13, 09 at 9:23 am

    I understand it now,
    Thanks!

  5. Christine Mao said:

    Sep 20, 09 at 8:46 pm

    This was very easy to understand, however, step 2 shows the 4% as 04 instead of a decimal in front of.04.

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