Indigo is organizing textbooks on her bookshelf. She has a Spanish textbook, a math textbook,
and a physics textbook. How many different ways can she line the textbooks up on her
bookshelf?
Answer
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Indigo can arrange her three textbooks in different sequences by calculating the permutations of the three books. The formula for permutations is , where is the number of items to arrange. In this case, it’s . So, there are 6 different ways she can line them up!

For example, she could have them in the following orders: Spanish-Math-Physics, Spanish-Physics-Math, Math-Spanish-Physics, Math-Physics-Spanish, Physics-Spanish-Math, and Physics-Math-Spanish. Each arrangement presents a unique way to organize her collection!