Hello, Phodot!

The probability of being born on a Friday the 13th is 1/214.

Assume the days of people's birth are independent of each other.

(a) You meet two new friends. What is the probability that

both new friends were born on a Friday the 13th?

I got this one, just use the multiplication rule so: . Right!

(b) You meet 31 new friends; what is the probability that

at least one of these new friends was born on a Friday the 13th?

The opposite of "at least one" is "none."

The probability thatwere borh on Friday the 13th is: .none

Therefore: .