p_history = 0.07 p_nonhistory = 1 - p_history p_nonhistory_3 = p_nonhistory**3 p_history_4_or_more = p_nonhistory**3
Confused about the answer to the second part of this exercise (pasted below).
A library has a stock of 2,701 books. If we sample randomly and with replacement a book from the library, the probability of taking a history book is 0.07 every time we perform the random experiment. Calculate:
- The probability that we don’t take any history book in the first three draws. Assign your answer to
- The probability that it takes four draws or more to get a history book from the library. Assign your answer to
I checked the solution for #2. It said 1 - p_nonhistory_3
I am not seeing the logic. It seems to me that, for it to take 4 or more draws to get a history book, the only condition that has to be met is that a history book was not drawn in the first 3 draws. Which would make the answer parts 1 and 2 equivalent. The stated answer is (1 - p_nonhistory_3). but that expression would be the probability that a history book is drawn one or more times in the first 3 draws, which would mean it did NOT take 4 or more draws to get a history book. What am I missing?