To be a 3 digit palindromic number, it must be of the form aba.
I assume that a 3 digit number must be at least 100 (so that 020 for example does not count as a 3 digit number):
Thus there are 9 x 10 = 90 three digit palindromic numbers.
There are 90 palindromic numbers.
Twenty.
19
a 8-digits palindromic number is a number consisting of a 4-digits number written and then written backward, i.e. 1234 4321 so there are as many palindromic 8-digits numbers as 4-digits numbers so from 1000 to 9999, so there are 8999 palindromic 8 digits number (I assumed that 00011000 is not to be considered as a valid 8 digit number)
266, 267, 268
There are 90 palindromic numbers.
There are 90 palindromic numbers between 100 and 1000
There are 900 three-digit numbers, ranging from 100 to 999.
infinite
There are not just 13 non-palindromic numbers. Most numbers are non-palindromic.
There are 900000 of them.
90
9
1089
10
1089
Twenty.