Austin is organizing textbooks on his bookshelf. He has an English textbook, a math textbook, a physics textbook, and a writing textbook. How many different ways can he line the textbooks up on his bookshelf?
There are 4 textbooks, so there are 4 options for which one goes first. Once the first book is chosen and placed on the shelf, there are 3 options left for which book goes second. Continuing in this way, the number of options for which book goes next decreases by 1 for each book placed on the shelf until only 1 option is left for the last book. Therefore, the total number of ways Austin can line up his textbooks is:
4 × 3 × 2 × 1 = 24
There are 24 different ways Austin can line up his textbooks on his bookshelf.