Final answer:
To calculate the probability that you and your 2 friends will win the concert tickets, divide the number of favorable outcomes by the total number of possible outcomes. In this case, the probability is 1/84.
Step-by-step explanation:
To calculate the probability that you and your 2 friends will win the concert tickets, we need to determine the number of favorable outcomes and the total number of possible outcomes.
There are 9 people in the group, including you and your 2 friends. So, the total number of possible outcomes is 9 choose 3 (combination) which is equal to 84.
The number of favorable outcomes is the number of ways you and your 2 friends can be chosen from the group of 9, which is 3 choose 3 (combination) which is equal to 1.
Therefore, the probability that you and your 2 friends will win the concert tickets is 1/84.