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Selecting (9) students from (12) students is equal to not selecting how many students from (12)?

Answer and explanation

Correct answer: 3

If 9 students are selected from 12, then 3 students are left unselected. Hence, \(\binom{12}{9}=\binom{12}{12-9}=\binom{12}{3}\). Option 9 represents the number selected, not the number unselected. Exam tip: use the identity \(\binom{n}{r}=\binom{n}{n-r}\) in combination questions.

Related tags

CombinationsBinomial CoefficientsComplementary SelectionClass 11 MathematicsPermutations And CombinationsMathematicsClass 11 Mcq

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