Question

An unbiased die is thrown seven times. Find the probability of throwing it at least five six's.

Answer 1

Use binomial distribution.
P(r)=nCr*(p^r)(q^(n-r))

n=7
p=1/6
q=1-1/6=5/6

we need to calculate
P(5)+P(6)+P(7)
P(5)=7C5*(1/6)^5*(5/6)^2
=0.001875
P(6)=1.25*10^-4
P(7)=3.57*10^-6

Answer 2

0.005