Binomial probability: multiple-choice tests

[peggyskold]

Just when I was thinking I was getting this stuff I am once again confused. Anyone can tell me how to set this up:

A multiple-choice test has 15 questions with each having 4 possible answers wth one correct. Assume a student answers every question?
What is the probability of geting exactly 5 correct answers?

For this part ,So far I come up with one out of four answers are correct 1/4 =0.25 probability of guessing one correct answer. I know 15 questions has to play a role here so...with 5 correct answers out of 15 questions..Am I close??? Get lost in here.

What is the probability of getting less than 6 correct answers?
so here would we subtract 6 from 15 and would be 9/15 correct answers out of 15 questions? Lost again
Help anyone.

Thanks
Peggy

 

[royhaas]

Re: Binomial probability

Use the formula for binomial probabilities with \(\displaystyle n=15, p=1/4\). You should have a table in your textbook, probably as an appendix. The formulas should also be in your book.

 

[peggyskold]

Re: Binomial probability

I will try this--thank you so much!

I just wanted to take a moment to say "Thank you" to those out here. It is really helping me! Thanks
Peggy