statistic
posted by tanya on .
Quiz has 6 questions. Each question has five possible answers,
only one of each 5 answers is correct.
If student randomly guesses on all six questions,
what is the probability to answer 2 questions right?
Tip: first, you have to define parameters of Binomial distribution:
n  how many trials/questions do you have
p  probability guessing right answer to each question
x  how many successes do you expect.
Then use Appendix Table or Excel function for Binomial distribution.
Answer

Assuming the 6 questions are independent,
n=6 (questions)
p=probability of guessing the right answer (1/5)
x=exactly the number of successes over the 6 questions (2).
Look up the appendix table, or the Excel function to calculate the probability.
Alternatively, use the formula:
P(x) = C(n,x)*p^{x}*(1p)^{nx}
Where C(n,x) represents the number of combinations of taking n things, x at a time. 
.8

on a test midterm exam each multiple choice question provides five possible answers. what is the probability of randomly guessing three consecutive questions correctly?

.324

.24576
You're welcome 
0.24576

answer 0.24576

p(x=4)=0.24576

p(x=4) = binompdf(6, 1/5, 4) = 0.2458