A stoplight at the corner of Lincolnway and Duff Avenue is red 20% of the time. For someone who drives through this stoplight 10 times a week, what is the probability that they will stop at least three times?

The experiment consists of 10 bernoulli (either true or false) experiments over one week.

The probability of success p is 0.3 (so failure, q=0.7)
The probability does not change throughout the week.
This is a binomial distribution, where the probability of r success out of n trials is
P(n,r)=C(n,r)*p^r*q^(n-r)
and C(n,r) is combination function given by
C(n,r)=n!/(r!(n-r)!)

Thus
P(10,0)=1*0.3^0*0.7^10=0.028
P(10,1)=10*0.3*0.7^9=0.121
P(10,2)=45*0.3^2*0.7^8=0.233
and probability of stopping at least three times is
1-(P(10,0)+P(10,1)+P(10,2)
=0.617