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Homework Help: Venn diagram and sample space

  1. Dec 18, 2017 #1
    I need some help in checking my work, especially #4. Problem: You have a set of 10 cards numbered 1-10. You choose a card at random. Event A is choosing a number less than 8. Event B is choosing an even number. Draw a Venn Diagram and calculate each of the following probabilities:

    1) P(A) = 77.8%
    2) P(B) = 55.6%
    3) P(A intersection B) = 33%
    4) P(A union B) = 100%
    5) P(A complement) = 22.2%

    For #4, my calculations were P(A union B) = P(A) + P(B) - P(A and B). Did I calculate something wrong here?
  2. jcsd
  3. Dec 18, 2017 #2


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    This should be moved to the homework forums.

    Did you draw a picture?

    I don't understand your problem 4. What is the probability of drawing a 9?
  4. Dec 18, 2017 #3


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    I moved the thread to our homework section.

    You have 10 cards with equal probabilities (I guess), where do you get all the odd percentage values from?
    The mistake with (4) follows from wrong answers to the previous parts. Alternatively, you could simply count how many cards are in (A union B).

    All your answers would be correct if 9 wouldn't be part of the cards.
  5. Dec 18, 2017 #4


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    For #1, it looks like you are dividing the number of cards in A by 9. Why? There are 10 cards in all. Same for #2 and others.
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