Results 1 to 2 of 2

Math Help - Probability: Is it conditional?

  1. #1
    Newbie
    Joined
    Apr 2009
    Posts
    1

    Probability: Is it conditional?

    I'm having trouble telling if this is meant to be conditional probability or not.

    A chart showing results from a survey of adults regarding tattoos is shown below. Assuming the data are representative, estimate the probabilities that:
    a) A randomly selected person has a tattoo, and
    b) A randomly selected person of age between 18 and 29 has a tattoo.

    Data:
    At least one tattoo:
    Age 18-29: 18
    Age 30-50: 6

    No tattoo:
    Age 18-29: 32
    Age 30-50: 44

    For part a, I simply did the probability that someone would have a tattoo (any age). 18+6 = 24, or 24% probability that someone would have a tattoo. I think that's correct.

    Part b is where I start to get a little confused. I thought I might need to use conditional probability, P(age 18-29 | at least one tattoo), which would be 18/24=75%. Then I started to question it, and wondered if it was maybe P(at least one tattoo | age 18-29), which would be 18/50=36%.

    ...now I'm wondering if the answer isn't just 18% (because 18 out of 100 people will be 18-29 and have one tattoo). I suppose that could be right, since the question never states "given that," which would signify conditional probability. Any help is greatly appreciated.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Member SengNee's Avatar
    Joined
    Jan 2008
    From
    Pangkor Island, Perak, Malaysia.
    Posts
    155
    Quote Originally Posted by jacobaf20 View Post
    I'm having trouble telling if this is meant to be conditional probability or not.

    A chart showing results from a survey of adults regarding tattoos is shown below. Assuming the data are representative, estimate the probabilities that:
    a) A randomly selected person has a tattoo, and
    b) A randomly selected person of age between 18 and 29 has a tattoo.

    Data:
    At least one tattoo:
    Age 18-29: 18
    Age 30-50: 6

    No tattoo:
    Age 18-29: 32
    Age 30-50: 44

    For part a, I simply did the probability that someone would have a tattoo (any age). 18+6 = 24, or 24% probability that someone would have a tattoo. I think that's correct.

    Part b is where I start to get a little confused. I thought I might need to use conditional probability, P(age 18-29 | at least one tattoo), which would be 18/24=75%. Then I started to question it, and wondered if it was maybe P(at least one tattoo | age 18-29), which would be 18/50=36%.

    ...now I'm wondering if the answer isn't just 18% (because 18 out of 100 people will be 18-29 and have one tattoo). I suppose that could be right, since the question never states "given that," which would signify conditional probability. Any help is greatly appreciated.

    You should be more confidence.
    The question (b) has give you a condition that "person of age between 18 and 29", that means you should only looking at the person of age between 18 and 29. Therefore the answer is 36%.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Replies: 0
    Last Post: July 22nd 2011, 01:39 AM
  2. Conditional Probability using the Law of Total Probability
    Posted in the Advanced Statistics Forum
    Replies: 1
    Last Post: October 7th 2010, 03:01 AM
  3. Conditional Probability
    Posted in the Statistics Forum
    Replies: 3
    Last Post: December 16th 2009, 06:27 PM
  4. Continuous probability - conditional probability
    Posted in the Statistics Forum
    Replies: 1
    Last Post: October 1st 2009, 01:21 AM
  5. Conditional Probability #2
    Posted in the Statistics Forum
    Replies: 2
    Last Post: April 23rd 2009, 07:07 AM

Search Tags


/mathhelpforum @mathhelpforum