Probability Essentials

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 Practice Questions

The questions below refer to a survey I did of my Introductory Statistics students. They were asked whether they supported Bush for President in the 2004 elections, and were given an "undecided" options. Realize that "no" does not mean "Kerry", but "Not Bush."
  No Yes Undecided Total
Female 25 10 17 52
Male 28 14 16 58
Total 53 24 33 110

The questions below assume that we are selecting people from this collection at random.

1. Are undecided students more likely to be men than women?

2. Is gender independent of support for Bush?

 

Students were also asked if they supported gay marriage.

  No Bush Yes Bush Undecided Bush Total
No gay mrg. 16 11 7 34
Undecided 12 4 10 26
Yes gay mrg. 25 16 9 50
  53 31 26 110

3. Among Bush supporters, which is the most likely opinion on gay marriage?

4. Are opinions on gay marriage independent of support for Bush?

5. A political pollster mistakenly assumes that every Bush supporter must be opposed to gay marriage. If the pollster selects a Bush supporter from this classroom, what's the probability the person supports gay marriage? Can you also solve this using a tree diagram?

For solutions, click here.