Yahoo Answers is shutting down on May 4th, 2021 (Eastern Time) and beginning April 20th, 2021 (Eastern Time) the Yahoo Answers website will be in read-only mode. There will be no changes to other Yahoo properties or services, or your Yahoo account. You can find more information about the Yahoo Answers shutdown and how to download your data on this help page.
Trending News
Probability help with a True/False Test?
Okay, so I'm studying for my math test and I have NO CLUE how to do some of these problems.
The situation is that a girl is taking a test with 5 questions. Each question has 5 answers listed "a-e". A new student is taking a test on his first day of school and has no prior knowledge of the material. (So he is COMPLETELY guessing)
What is the probability that he only misses 2 questions?
What is the probability that he misses more than 2 questions?
1 Answer
- M3Lv 71 decade agoFavorite Answer
to get this problem, you must be knowing about the binomial distribution.
the one here has parameters n = 5, p = 1/5, q = 1- p = 4/5
formula for k successes in n trials is
P[k] = nCk * p^k * q^(n-k)
qa
miss 2 questions means get 3 right,
P[3] = 5C3 * [1/5]^3 * [4/5]^2
= 10*1*16/3125
= 32/625 or 5.12%
---------------------------
qb
misses more than 2 q's means gets 0,1 or 2 right
calculate P[0] + P[1] + P[2]
= 5C0*[1/5]^0 *[4/5]^5 + 5C1*[1/5][4/5]^4 + 5C2*[1/5]^2 *[4/5]^3
= [4^5 + 5*4^4 + 10*4^3] / 5^5
= 2944 / 3125 or 94.208%
----------------- -------------------
