10 red marbles and 10 blue marbles are placed into a bag. All mixed up and randomly selecting one after the other with replacement, until a red marble is selected.
a) What is the probability that the first time that a red marble is pulled is on 6th try? My answer:
Probability of drawing a red marble on the 6th try is: (.5)^5 * (.5)^1 = 0.015625
b) On average, how many marbles will we have to pull in order to get a red marble? My answer: 1/p = 1/.5 = 2
If my answer to question (b) is correct, is this what we call math expectation.