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The lock opens only if the 4 digits are arranged in a sequence with no:
ARepetition
BReputation
CResolution
DReservation
Answer & Solution
Correct answer: A. Repetition
1. A constraint on the arrangement changes how many sequences exist.
2. Here no digit may be used twice.
3. The lock can be opened if 4 specific digits are arranged with no repetition.
4. That is what makes it a permutation problem.
_Source: NCERT Class XI Mathematics, Ch 6 'Permutations and Combinations'_
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