homework help SOS!!!
Message posted by Linda (via 207.44.115.169) on October 11, 2001 at 10:44 PM (ET)

The problem: a professor wants to give a 20 question true/false quiz to determine who has read an assigned novel;she wants to choose a passing grade such that the probability of passing a student who guesses on every question is less than .05. What score should she set as the lowest passing grade?
I'd appreciate any help!! Thank you!

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Re: homework help SOS!!!
Message posted by Tomi (via 154.32.143.231) on October 12, 2001 at 2:44 AM (ET)

If a student guesses, then they have a 0.5 probability of getting a question right. Let's call the number of correctly guessed answers X. Now it is possible to work out the probability that X = 0, X = 1 etc using a huge tree diagram or by using the Binomial distribution. X ~ B (20, 0.5).

If you work out P(X=20) you will find that it is very small. Add it to P(X=19) and it will be a bit larger. Continue until you have a number just less than 0.05, and you have solved the problem. Of course, you could always use cumulative frequency tables for the binomial distribution.

Re: homework help SOS!!!
Message posted by Linda (via 207.44.115.169) on October 12, 2001 at 8:30 AM (ET)