Question

The number of $7$ digits palindrome passwords that can be created is

• A. $9000$
• B. $10000$
• C. $9990$
• D. $9999$

Answer 1

The correct option is B $10000$

Let the $7$ digits palindrome password is: $ABCDCBA$
Now, $A$ can be filled in $10$ ways (zero is also included for password),
$B$ can be filled in $10$ ways,
$C$ can be filled in $10$ ways and
$D$ can be filled in $10$ ways
$\therefore$total such passowords $=10\times 10\times 10\times 10=10000$