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
6
B
8
C
10
D
12
Correct Answer: Option C
Explanation
To solve this, we need to find how many valid PINs exist. If there are 10 valid PINs, then in the worst case (maximum attempts), I would have to try all 10 to find the correct one wi