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Combinations: selections where order doesn't matter
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Learn it Choosing r items from n when order doesn't matter: nCr = n!/[r!(n − r)!]. Use 'and' → multiply, 'or' → add for combined selections.
Example: A committee of 2 teachers and 3 students from 5 teachers and 10 students.
- 5C2 × 10C3 = 10 × 120.
- = 1200 committees.
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