Intro Stats Problem.

[stats151]

A student takes a true or false test with 15 questions. He guesses on every question.

1) Find the probability that he gets atleast 1 question right
2) Find the probability he gets 60% or higher.

I am stuck. I know it is something with perms and coms. Any help would be great.

 

[Dason]

Do you know about the binomial distribution?

 

[stats151]

No, it isn't in the chapter of this textbook, so I'm assuming its not used. Im just trying to read the textbook examples and try to figure it out but I can seem to get any answer that makes sense.

 

[Dason]

Well the binomial distribution makes things easier it looks like this question is basically asking you to derive and use the binomial distribution which is entirely possible based on first principles.

Hint for question 1: Can you figure out the probability that they get 0 correct is?

 

[stats151]

Okay so I'm doing 15 choose 15. Then 2^15. So he has a 1/32768 chance of getting 0 right.

 

[stats151]

I was wrong binomial distribution is in the chapter its just further into it.

 

[stats151]

but its not at the part where the question so i feel like you aren't suppose to use it.

 

[Outlier]

One of these has got to work for you
http://www.google.com/search?q="bin.....1ac.1.34.heirloom-serp..0.2.221.GNdGxsBFPgI
and better searches will give you more-to-the-point results.

You can also do this brute-force with a spreadsheet. With cutting and pasting it's not too bad because the pattern repeats, but stock up on coffee.
Writing a small program is another way.