Zero! Who could possibly a Red Sox Fan when the Yankees are in town? Let them mourn the loss of the Babe forever!
Now you have a group of 20 and a group of 15. What you are being asked is what is the smallest number that you could find that can be divided evenly by 15 and 20? Is it 20 * 15=300 or is it something smaller.
The way to solve this is to write out the factors of 15 and 20.
15 = 3*5
20 = 2 * 2 * 5
So the smallest number is
one 3
two 2s
one 5 Don't count these 5s twice.
LCM = 3 * 2 * 2 * 5
LCM = 60.
The smallest group she could see of Yankee Fans and Red Sox Fans is 60 if they both must be equal.
Answer 60 Red Sox Fans.