First grade class of 9 girls and seven boys walk into class

First grade class of 9 girls and seven boys walk into class in alphabetical order by last name, what is the probability that three girls are the first to enter the room.

Solution

There are 9 girls + 7 boys each with alphabetical order by last name

n(S) = 9 +7 = 16

So, probability of first three girls = (9/16)(8/15)(7/14)

= 504/3360

= 0.15