Math Is Fun Forum

Skyblast72

Member

Registered: 2012-09-30

Posts: 16

Probability of guessing questions on a test

Probability question:

A student takes a 19-question, multiple choice exam with three choices for each question and guesses on each question.  Find the probability of guessing exactly 8 out of 19 correctly.

I used 19C8  so n=19 x =8 p=.33 and q=.67 but I can't come up with any of the answers that are on my homework. 

I am a beginning statistics/probability student.  Showing your work would be helpful to me so I can learn how to do this stuff.  Thanks for any help you are able to give, I appreciate it!

Bob

Administrator

Registered: 2010-06-20

Posts: 10,621

Re: Probability of guessing questions on a test

hi Skyblast72,

That seems to be the right method to me.  I made that 0.133182...

How about you?

Bob

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Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Probability of guessing questions on a test

Hi;

With n = 8 and p = 1 / 3 and trials = 19.

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In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

Skyblast72

Member

Registered: 2012-09-30

Posts: 16

Re: Probability of guessing questions on a test

THANK YOU!! I see where I messed up now.