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Subjects
Class 11MathematicsPermutations and CombinationsFundamental principle of countingHard
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A lock has (4) positions. Each position can have any digit from (0) to (9), but exactly (2) positions must contain the digit (7). How many lock codes are possible?

Answer and explanation

Correct answer: (486)

Choose the (2) positions for (7) in (\binom{4}{2}) ways, and each remaining position has (9) choices. For exactly conditions, exclude the fixed digit from remaining places.

Related tags

CodesExactlyCountingFundamental Principle Of CountingPermutations And CombinationsMathematicsClass 11 Mcq
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