How to Find the Probability of Group Members Choosing the Same Thing

Probability 7 Comments

These probability questions give you a group, and ask you to calculate the probability of an event occurring for all of a certain number of random members within that group.

Sample Problem: “There are 200 people at a book fair. 159 of them will buy at least one book.  If you survey 5 random people coming out of the door, what is the probability they all will have purchased one book?”

This type of question can be answered in couple of short steps.

Step 1: Convert the data in the question to a fraction. For example, the phrase “159 people out of 200″ can be converted to 159/200.
Step 2:Multiply the fraction by itself. Repeat for however many random items (i.e. people) are chosen. In our example, we have 5 people surveyed, so we want:

159/200 x 159/200 x 159/200 x 159/200 x 159/200 = 0.3176

That’s it!

Related posts:

  1. How to find the probability of selecting a person from a group or committee
  2. Finding the Probability of a Random Event Probability
  3. How to figure out the probability of picking from a deck of cards in probability and statistics
  4. How to find the probability of a simple event happening
  5. How to find the probability of an event NOT happening
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7 Responses to “How to Find the Probability of Group Members Choosing the Same Thing”

  1. Sarah M. Joyner said:

    Sep 18, 09 at 4:27 pm

    I think is a typo. In step 1 you have convert to 159/100, I am guessing that it should be 159/200 since the rest of the explanation uses that.

  2. Stephanie said:

    Sep 19, 09 at 1:22 pm

    You are totally right–thanks for spotting that!
    Stephanie

  3. Jennifer Thomas said:

    Sep 20, 09 at 12:20 pm

    This was very helpful. When following the example in the book, I got lost. Your steps were much easier to understand.

  4. Kalynn Grabau said:

    Sep 21, 09 at 8:43 am

    Wow, that is really simple and easy to do. I think the book makes things look a little more difficult than they really are..

  5. Lisa Barcomb said:

    Sep 25, 09 at 8:55 am

    yeah the book does seem to make it harder then it really is. I like this blog thing it really breaks the information down to where you can understand it since I am not a math major. And I tend to have trouble with math from time to time. Especially when it comes to word problems. I think what I do is put more into it then what it is and then I get myself all confused and lost. But the way this problem is, is really easy to understand when they are broken down like this step by step.

  6. Stephanie said:

    Sep 25, 09 at 9:05 am

    I’m really glad this is helping!

    Stephanie

  7. Vanessa DuBarry said:

    Dec 14, 09 at 10:17 pm

    I really liked this example, and it really helps better then the book overall this is really helpful.

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