Question

A letter lock consists of three rings each marked with fifteen different letters; find in how many ways it is possible to make an unsuccessful attempt to open the lock.

Answer 1

A letter lock contains three rings each marked with fifteen different letters

So, there can be $15\times 15\times 15$ number of attempts

$\therefore$ Total number of attempts $=3375$.
Now, there can be only one successful combination.
$\therefore$ Total number of wrong attempts $=3375-1$
$=3374$