Step-by-step explanation:
The numbers 1 to 9 are 9 digits
The numbers 10 to 99 are 90*2 = 180 digits.
You have written 189 digits and must write another 1000 - 189 = 811 digits.
Every number from 100 to 500 have 3 digits.
811/3 = 270 1/3
So you write 270 numbers: 100 to 369
And then you will write the first number from 370 (the 1000th digit). This digit is 3.