CSAT 2022

Q. There is a numeric lock which has a 3-digit PIN. The PIN contains digits 1 to 7. There is no repetition of digits. The digits in the PIN from left to right are in decreasing order. Any two digits in the PIN differ by at least 2. How many maximum attempts does one need to find out the PIN with certainty?

a.    8
b.   8
c.    10
d.   12
Correct Answer: c.    10

Question from UPSC Prelims 2022 CSAT Paper

Explanation :

Numeric Lock 3 digit PIN Combinations

All Possible Values for a 3-digit PIN are 753, 752, 751, 742, 741, 731, 642, 641, 631, 531.
So, the maximum number of attempts one need to find out the PIN with certainty is 10.

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