Aerospace engineer turned baseball writer Eric Walker writes that the most important statistic for a baseball player

Question:

Aerospace engineer turned baseball writer Eric Walker writes that the most important statistic for a baseball player is “on-base percentage” which basically measures “the probability that a batter will not make an out”. Suppose all the players for the Orchard Park Mangos have an on-base percentage of .350 (35%). In a given inning, how likely is it that
a. Only three batters come to the plate; that is, how likely is it that only three batters take a turn batting?
b. Exactly fve batters come to the plate?
c. At least seven batters come to the plate?