Question

There are 9 white balls and 1 red ball in the box. What is the probability to pick a red ball at least once in 10 extractions (if the balls are returned back after each extraction)? How many extractions should be done to pick the red ball with the probability not less than 0.9?

Answer 1

Answer: 1 − ((9/10)^10) ≈ 0.6513; lg(0.1)/lg(0.9) ≈ 22