### Counting with Identical Items

Lesson by Mike McGarry
Magoosh Expert

Summary
The content provides a comprehensive guide on calculating arrangements involving identical items, a crucial concept for GMAT preparation.
• Introduces the concept of arranging n unique items and extends it to scenarios involving identical items, requiring a special approach.
• Explains the method to calculate arrangements when some objects are identical, using the factorial formula adjusted for identical items.
• Illustrates the concept with examples, including arranging books on a shelf and the letters in the name 'Mississippi', to clarify the calculation process.
• Offers a practice problem to apply the learned concept, reinforcing the method of dividing the total factorial by the factorial of the number of identical items.
• Summarizes the key rule for calculating arrangements with identical items, emphasizing the importance of listing and counting as a strategy in solving counting problems.
Chapters
00:00
Introduction to Arrangements with Identical Items
00:28
Calculating Arrangements with Identical Items
03:17
The Mississippi Rule
04:31
Practice Problem and Summary