Answer:
21/55
Step-by-step explanation:
Since there are already 2 girls on the relay team, what is left is to select 2 individuals be it a girl or a boy from the remaining 7 boys and 4 boys.
This can be done in 11C2 ways, and this equal 55 ways.
Now, we were told that we want exactly 2 boys on the team to join the other 2 girls already on the team. This mean we select 2 boys from the 7 boys. This can be done in 7C2 ways and this equals 21 ways.
Our probability is now 21/55
