What's the answer?

I have a friend who was a few years ahead of me as an assistant professor at Illinois.  His area of specialization is energy economics.  (Think big oil.)  He left Illinois to go to the University of Houston.  He subsequently went to SMU and is a chaired professor there.  We stay in touch, primarily via a mutual colleague.  Recently the topic is baseball.  He is quite an Astros fan now.  He wrote:

"The Yanks look like they could be the Astros/Cubs of 2018. Quick quiz: if the two teams are evenly matched, which is more likely, a 6 or 7 game series?'

What is the answer to this question?