Question

A letter lock consists of three rings each are marked with 10 different letters. Find the number of ways in which it is possible to make an unsuccessful attempts to open the lock.

Answer 1

Total number of attempts $=10\times 10\times 10=1000$

Number of unsuccessful attempts $=$ Number of total attempts $-$ Number of successful attempts

$$\begin{gathered} =10\times 10\times 10–1 \\ =1000–1 \\ =999. \end{gathered}$$

Therefore, the number of ways in which it is possible to make an unsuccessful attempts to open the lock is $999.$