[jay_shark]

This is a binomial distribution with p=20% , q=80% .

p=success
q=failure

Let x be a random variable of making a sale .

P(x=7) = 12c7(0.2)^7*(0.8)^5 There are 12 choose 7 ways of making 7 successful sales from 12 homes selected .

Similarly
P(x=8) =12c8(0.2)^8(0.8)^4

Continue in this manner by adding P(x=7)+P(x=8)+P(x=9) +P(x=10) +P(x=11) + P(x=12) which is equivalent to P(x>6)

The formula is P(X=x) = nCx*P^x*q^(n-x) , n=12 in this case