Every day Jo practices her tennis serve by continually serving until she has had a total of 50 successful sent If each of her serves is, independently of previous ones, successful with probability .4, approximately what is the probability that she will need more than 100 serves to accomplish her goal?
Imagine even if Jo is successful that she continues to serve until she has served exactly 100 times. What must be true about her Ant 100 serves if she is to reach her goal?