View Full Version : i hope i make JohnM and quark proud
10-10-2005, 05:37 PM
okay i managed to do a bonus question on my "take home test" (which is kinda :) .
I just want to see if I did it right and answered it right bare with me....
IF I DID NOT DO OR ANSWER IT RIGHT DO NOT TELL ME HOW!!!
A student takes a 9 question multiple choice test by guessing. Each question has 5 choices. What is the probability that at least 4 are correct?
n! x (n-x)
_________ *p * q
using these values,
i got 26%
please tell me I did this correct
And I do want to know how you are making out of this website, because i told everybody in my statistics class!!!!!
10-10-2005, 06:17 PM
We're always proud of students who try!:)
With this problem, you started on the right track. Make sure the binomial formula includes p^x and q^(n-x).
p = probability of success
q = 1-p
You need to think how "success" is defined in this problem - it's the probability of getting 1 question correct by guessing the correct answer out of 5 choices.
Then you need to find the probability of getting 0 correct, 1 correct, 2 correct, and 3 correct. Add these up, then subtract this sum from 1.
In a binomial probability distribution (any distribution, for that matter), the sum of all the probabilities equal 1. So, the probability of getting 4 or more correct is equal to 1 minus the probability of getting 3 or less.
10-10-2005, 07:08 PM
Since there are five choices in each question, p=1/5, and q=4/5.
10-10-2005, 07:22 PM
is this it?????????
10-10-2005, 07:44 PM
The probability of:
0 correct = 0.1342
1 correct = 0.302
2 correct = 0.302
3 correct = 0.1762
Add these up and subtract the sum from 1.
The answer is 0.0856, or around 8.5% chance of guessing 4 or more questions correctly.
Think it through - if you had to completely guess on 9 questions, and the probability of getting any particular question correct is only 20%, it's going to be really hard to guess 4 or more correctly.
10-10-2005, 08:33 PM
i did not have to change p=1/5 and q=4/5
i just had to change the
n! / (n-X)X! formula
and x=0, x=1, x=2, x=3, for each formula
and the p^n and q^(n-x)
i finally figured it out thanks sgain
p.s I am still stuck on the 175 words per minute,with a standard dev. of 20, the top 3% of the class is to receive a special award, what is the min
but do not tell me, you have helped me enough. I will get it and let you know what I come up with
thanks again quark and JohnM
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