A student takes a multiple choice exam with 10 questions, each with four possible answers. A passing grade is 60% or better. Suppose that the student was unable to find time to study for the exam and just guesses at each queston. Find the probability that the student:

a. gets at least one correct
b. passes the exam
c. receives an A (90% or higher)
d. How many do you expect him to get right?
e. Standard deviation of correct questions?

Step-by-step explanation:

Let r = .25 probability of getting question right. and w = .75 prob getting it wrong.

since there are 10 questions, this will tell us what we want to know.

a)  1- doesn't get them all wrong.

   1-

  =1-.0563

  =.9437

b)  Probability of getting 6-10 answers right

=.0197

c) This means 9 or 10 answer should be right

=.00003

d) = 2.5 expected correct answers.

e) Standard deviation for a binomial distribution is

=

=

=1.369

d (5 x (-20)) * (100 x (0.7))

step-by-step explanation:

5÷1/100 * -.7 *-20

copy dot flip

5*100 * -.7 *-20

rearrange

5*-20   * 100 *-.7

-100   *-70

7000