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Aptitude Topics

Permutation-Based Probability

When managing large groups or sequential arrangements, listing out outcomes manually becomes impractical. Instead, we use combinations and permutations to count possibilities efficiently.

Fundamental Principles

Combination Formula nCr

Used when selection order does not matter: nCr = n! / [r!(n - r)!], where 'n' is the total pool and 'r' is the number of items being chosen.

Permutation Formula nPr

Used when selection order matters: nPr = n! / (n - r)!

Essential Formulation Tips

  • Use Combinations (nCr) for committee selections or drawing groups of balls, where order doesn't matter. Use Permutations (nPr) for seating arrangements or word formations, where order does matter.

Shortcut Execution Techniques

  • When an arrangement problem requires certain items to always stay next to each other, tie those items together and treat them as a single structural block during calculations.

Contextual Inquiries (FAQs)

Q: What does the exclamation mark symbol (!) mean in these formulas?

A: