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Math Help - Practice Test Question (Answer is Right or Wrong?)

  1. #1
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    Practice Test Question (Answer is Right or Wrong?)

    I am tutoring a student. His teacher provided a sample TAKS test with this question.

    A census shows that on Timís block the families contain 3, 4, 4, 0, 1, 2, 0, 2, 2 children respectively.
    If a family on this block is randomly chosen, what is the probability it is Timís family?

    The correct answer is given as 7/9. 7 - the number of families with children in them; 9 - the total number of families on the block.

    But that is the probability of selecting a family with a child. 7 - number of families with children. 9 - total number of families.

    The probability of selecting Tim's family from a random selection of families on the block is 1 - number of Tim's families / 9 total number of families (1/9).

    I'm double checking. Is 7/9 correct?
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  2. #2
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    Yes although it's a poorly written question since we're not told whether Tim is classed as a child or a parent
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    Yes what? Is it 7/9 or 1/9?

    Even if the question states Tim is a child, there is only 1 desired outcome. Only 1 family contains Tim.

    If the question were "Tim is a child. What is the probability of selecting a family that could contain Tim?" then 7/9 would be correct.

    But if there is only one desired result, the specific family that contains Tim, then it's either 1/9 or 1/7 (if the problem indicates Tim is a child.)
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    I would say 1/7 because Tim is only in one family and there are 7 families with children
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    The probability that a family chosen at random is Tim's is 1/9.

    I'm assuming all families are equally likely to be chosen. Ideally, this should be part of the problem statement.
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  6. #6
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    "I would say 1/7 because Tim is only in one family and there are 7 families with children"

    The problem doesn't state Tim is a child.

    "I'm assuming all families are equally likely to be chosen. Ideally, this should be part of the problem statement."

    The problem states a family is randomly chosen. That means all families are equally likely to be chosen.
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