Question

A letter lock consist of three rings each marked with $10$ different letters. No of ways to make an unsuccessful attempts to open the lock is:

• A. $899$
• B. $999$
• C. $479$
• D. $568$

Answer 1

The correct option is B $999$

$firstringhas10options$

$secondringhas10options$

$thirdringhas10options$

$\therefore permutation=10\times 10\times 10=1000$

$no.ofwaysofunsuccessfulattempt=(1000-1)=999$