SOLUTION: On a test, if 22 questions have three choices each (one correct, two incorrect) and 3 questions have two choices each (one correct, one incorrect), what is the probability that a t

Algebra ->  Probability-and-statistics -> SOLUTION: On a test, if 22 questions have three choices each (one correct, two incorrect) and 3 questions have two choices each (one correct, one incorrect), what is the probability that a t      Log On


   

Question 857043: On a test, if 22 questions have three choices each (one correct, two incorrect) and 3 questions have two choices each (one correct, one incorrect), what is the probability that a test taker guessing randomly on each question will receive a test grade of B or better (80 points or higher) ?

This question really threw me for a loop - I know how to use the binomial distribution function to find the probability of one set of data (like if they were all multiple choice or just of the same number of answers), but there being two different kinds of questions confuses me. Any help would be greatly appreciated.
Answer by ewatrrr(24785) About Me  (Show Source):
You can put this solution on YOUR website!
 

Hi,

first of all 25 Questions(assuming each counts 4 pts) 

therefore: 20 or more correct would result in 80 points or higher.

Will get You started...

P(100) = (1/3)^22(1/2)^3   all right 

P(96) =  one wrong

the more ways it can happen .. the longer the string gets...final addition will have similar multiples...helps some

92 =  2 wrong Note: 3C1 = 3C2 = 3

88

84

80