Question 25
Initially a box has 2 black balls and 1 white ball. One black ball is added every 2 seconds from 0:02 through 1:00; one white ball is added at 17 and at 37 seconds. Draw one ball at 0:00, then wait 20 seconds between draws, drawing after the scheduled black-ball addition. Find the probability of drawing a white ball within one minute.
Source modeling note: the source does not explicitly state whether drawn balls are replaced or whether the one-minute endpoint is included. The answer below uses no replacement, includes the draw at 60 seconds, and performs each scheduled addition before the simultaneous draw; it matches the printed key under these stated assumptions.
Source modeling note: the source does not explicitly state whether drawn balls are replaced or whether the one-minute endpoint is included. The answer below uses no replacement, includes the draw at 60 seconds, and performs each scheduled addition before the simultaneous draw; it matches the printed key under these stated assumptions.