If you write the numbers 1, 2, 3, ..., 10, 11, 12, ..., 99, 100, ..., what is the 100th digit you write?
There are 9 1 digit numbers so that's 9 digits. After 49 2 digit numbers you are at 99 digits and the next digit you'll write is a 5 as in 59.
:D
The 100th digit is the first 5 of 55
1 to 9 = 9
54 - 10 + 1 =45 two-digit numbers.
9 + (45 * 2) ==99 - which is 4 of 54
99 + 1 =100th digit is the first 5 of 55.
