Calvin Goes to Ten Flags
Over the summer, Calvin, along with a group for friends, went to Ten Flags (an amusement park). There are 10 "must-ride" roller coasters. At the end of the day, everyone rode exactly 5 of these 10 rides (due to the dastardly long lines). Furthermore, any 2 different people rode at most 2 rides in common. What is the highest possible number of people in this group?
Details and assumptions
Calvin is to be included in the count. You should not exclude him from amusement parks.