SOLUTION: A student takes a 10-question, multiple-choice exam with three choices for each question and guesses on each question. Find the probability of guessing exactly 2 out of 10 correctl

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Question 979310: A student takes a 10-question, multiple-choice exam with three choices for each question and guesses on each question. Find the probability of guessing exactly 2 out of 10 correctly.
Answer by Edwin McCravy(20064) About Me  (Show Source):
You can put this solution on YOUR website!
A student takes a 10-question, multiple-choice exam with three choices for each
question and guesses on each question. Find the probability of guessing exactly
2 out of 10 correctly.
The formula for getting exactly x successes oout of n trials, when the
probability of getting 1 success in 1 trial is p, is

nCx%2Ap%5Ex%2A%281-p%29%5E%28n-x%29

Here n=10 questions, p = 1%2F10 = 0.1

10C2%2A%280.1%29%5E2%2A%281-0.1%29%5E%2810-2%29

%28%2810%2A9%29%2F%282%2A1%29%29%2A%280.01%29%2A%280.9%29%5E8

45%2A%280.01%29%2A0.43046721

0.1937102445

You can also get it on a TI graphing calculator:

2nd, VARS, scroll down to binompdf(, ENTER

10 trials, p is 0.1, x value is 2

binompdf(10,0.1,2)  ENTER

Or use a binomial table if you have one.

Edwin