Ralph writes the numbers 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, ... What is the 1000th digit that Ralph writes?
For digits 1-9, there is 1 digit.
For digits 10-99, there are 2 digits.
For digits 100-999, there are 3 digits.
Therefore, for digits 1-9, there is a total of 9 digits.
For digits 10-99, there is a total of 2((99-10)+1) = 2(90) = 180 digits
For digits 100-999, there is a total of 3((999-100)+1) - 3(900) = 2700 digits.
There is a total of 9 + 180 + 2700 = 2889 digits.
The 2889th digit is 0, so the 2890th digit must be 1.
The 110th digit after 2890th digit is 3.
Therefore the 1000th digit is also 3.
Tell me if I'm wrong.
1 - 9 gives us 9 digits
10 - 99 gives us [ 99 - 10 + 1] * 2 = 180 more digits
So far....we have 189 digits
So we need 1000 - 189 = 811 more
Let us suppose we only need 810 more
Dividing this by 3 = 270
So.....we need 270 3 digit numbers (including 100) to give us 810digits
We can solve this equation to find the last integer we need to write to get 810 more digits
[ n - 100 + 1] * 3 = 810
[n - 99] * 3 = 810 divide both sides by 3
n - 99 = 270 add 99 to both sides
n = 369
So after we write 369 we will have written 9 + 180 + 810 = 999 digits
The next integer we write will be the 1000th one
This is, obviously, 3