Calculators Won't Work! 1

Try the following multiplications:

$99 *$ any number, the sum of the digits is 18

$999 *$ any number, the sum of the digits is 27

$9999 *$ any number, the sum of the digits is 36

Now if you look carefully, there is a pattern which is look at how many 9s are there multiplied by 9 ;

Similarly, $999999999 *$ any number, the sum of the digits is $9 * 9 = 81$ .

Hence, the sum of digits of $p$ is 81