Probability that this stamp is one that you haven't seen before Suppose you have 4 stamps with probabilities 0.2, 0.4, 0.3, and 0.1, respectively. Each time you pick a stamp is independent of every other pick. Suppose you pick your 10th stamp. What is the probability this stamp is one you haven't seen before? How should I approach these kinds of problems? Should I do 1-prob(I've seen this stamp before)?

**A start:** Divide into cases, the $10$-th stamp is stamp A, and we have not seen it, it i stamp B and we haven't seen it, and so on.

The probability it is stamp A and we have not seen it is $(0.2)(0.8)^9$.