# Combinations

4 videos
2 skills
You are already familiar with calculating permutation ("How many ways could 7 different people sit in 4 different seats?"). But what if you didn't care about which seat they sat in? What if you just cared about which 4 people were in the car? Or put another way, you want to know how many combinations of 4 people can you stick in the car from a pool of 7 candidates. Or how many ways are there to choose 4 things from a pool of 7? Look no further than this tutorial to answer your questions.

### Intro to combinations

VIDEO 6:18 minutes
Sal introduces the basic idea of combinations.

### Combination formula

VIDEO 11:17 minutes
Sal explains the combination formula.

### Handshaking combinations

VIDEO 7:29 minutes
Sal figures out how different combinations of people can shake hands.

### Combination example: 9 card hands

VIDEO 7:42 minutes
Thinking about how many ways we can construct a hand of 9 cards

### Combinations

PRACTICE PROBLEMS
Introductory combination problems like if you have 5 friends and can pick 2 of them to join you on a boat ride, how many different groups of friends could you take with you?

### Permutations & combinations

PRACTICE PROBLEMS
Permutations and Combinations with overcounting