Another metro card?

Sharon, Uncle Dan and the kids ventured to New York for the day. We left early with the commuters and visited Ground Zero. It was an impact to view in person and the kids have a better understanding how 911 changed our lives. Our next stop was getting back on the subway. Everything was fine until the kids were stuck without us beyond the turnstile. We filled our metro card with more money, but nothing worked. We got another metro card and it worked for Sharon, but where's Dan? Of course Dan couldn't get through and he had to buy yet another metro card. Everyone gave high fives and we were on our way to the Natural History Museum. It was a lot of fun and the kids even pretended to be monkeys with their ancestors. We left Dan behind in New York with his friends. We'll have to ask him how many metro cards he bought.