A women arrives at an airport between 11 and 12 o'clock. she waits for her husband for 10 minutes and if he does not arrive, she hails a taxi (and he is in a lot of trouble!) Her husband shows up at the airport at some time between 11 and 11:50. He waits for 20 minutes and it his wife has not shown up, he goes home (and he is in a lot of trouble!). What is the probability that the woman rides home with her husband