Q1.

Ten numbers from 10 to 99 start with 3..... 30, 31, 32, 33, 34...

one number from 0 to 9 is 3,

nine numbers from 10 to 99 end with 3..... 13, 23, 33, 43....

33 is double counted.

Alternatively,

3 occurs in the 10's position 10 times......30, 31 to 39

and 3 occurs in the units position 10 times.....3, 13, 23, 33, 43...

33 is in both groups.