Problem 1 uses the binomial probability distribution. Check our Examples section - we have similar problems there.

p = 0.8

q = 1-p = 0.2

n = number of trials = 5

r = number of successes = at least 3 = 3 or 4 or 5

Problem 2 uses the concept of conditional probability, and by definition:

P(A|B) = P(A and B) / P(B)

event A = blonde hair

event B = glasses

P(A and B) = 2/25

P(B) = 9/25