Question

A letter lock consists of three rings each marked with $10$ different letters, the maximum number of unsuccessful attempt's to open the lock is

• A. $999$
• B. $899$
• C. $479$
• D. None of the above

Answer 1

The correct option is A $999$

Total number of different attempts possible is $=10\times 10\times 10=1000$
But among $1000$ attempts the lock gets unlocked only at once.

$\therefore$ maximum number of Unsuccessful attempts $=1000-1=999$