Question

Imagine taking a 10-question true or false exam. You randomly guess at each question. Don't do any calculations, just tell me your first impressions
a). Is this a binomial setting?
b) How many question do you think you would get correct?
c). How surprised would you be if you passed ( 6 out of 10 correct or better) the exam?
d) How surprise would you be if you got an "A" on the exam (9 or 10 out of 10)?

Answer 1

ell, I will just do the problem
a yes
p(right) = .5, (1 -pright)=.5
b half of them, 5
10 trials
p(k) = C(n,k) p^k (1-p)^(n-k)

p(6)=C(10,6) .5^6 .5^4 =210*.015625*.0625 = .205

p(7) = 120*.5^7*.5^3 = .117

p(8) = 45*.5^8 *.5^2 = .044

p(9) = 10*.5^9*.5 = .0098

p(10) = 10*.5^10 = .0005

so prob of six through ten = sum = .376 is probability of passing

p(9)+p(10) = .0005+.044 = .045