You just got free tickets to go on the boat ride and you can bring 3 friends unfortunately you have 5 friends who want to come along how many different groups can you take with you

Assuming that your own ticket is already secured.

From the 5 friends you can only choose 3.

The order in which these friends are chosen is not relevant. So this is a Combination problem.

Where the order is relevant the problem becomes a Permutation problem! 

So the answer is 5 combination 3.          =  ⁵C₃

⁵C₃  =  (5 * 4 * 3) / ( 3 * 2 * 1) = 10

You can take 10 groups of any 3 of your 5 friends.

Subtracting is the opposite of adding