Question 252818
Except for question e) these can be figured out by expansion of a binomial.
Let r = .25 probability of getting question right. and w = .75 prob getting it wrong.
(r+w)^10 since there are 10 questions will tell us what we want to know.
a)
1-w^10 doesn't get them all wrong.
1-.75^10
=1-.0563
=.9437
.
b)
6-10 answers right
r^10+10r^9w+45r^8w^2+120r^7w^3+210r^6w4
=.0197
.
c)
9 or 10 right
r^10+10r^9w
=.00003
.
d)
10 * .25 = 2.5 expected correct answers.
.
e)
Standard deviation for a binomial distribution is sqrt(n*p(1-p))
=sqrt(10*.25*.75)
=sqrt(1.875)
=1.369
.
Ed