Student: Maximum no of unsuccessful attempts, a thief can do in order to break a number locking system of 4 digits.\nOptions:\n(A) 9988\n(B) 9999\n(C) 9799\n(D) 9685\n(E) 6545.
Another student: Let's say, hmmm...

User
From 0 to 9999 there are 10000 four digit numbers\nSo maximum number of unsuccessful attempts = 10000 - 1 = 9999 Final answer: (B).
Assistant