Khan Academy Static

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.

4701_Intro_to_combinations.html

4702_Combination_formula.html

4703_Handshaking_combinations.html

4704_Combination_example_9_card_hands.html