I see your last line is : c(x) = 0.9(x^2-10)^2 + 101.1
Let y = x^2, then c(y) = 0.9(y-10)^2 + 101.1
Apparently, c(y) is a parabola, min is 101.1 when y = 10, max is infinity
So let x^2 = 10 -> x = sqrt(10) or -sqrt(10), min is 101.1, max is infinity
Is it 0.5? if so, the answer is 0.25%
if it is supposed to be just a 5 then the answer would be 2.5%
The final answer that i got from this was -x-13
Answer:
You wrote the numbers from 1 to 9: 9 digits.
You wrote the numbers from 10 to 99: 90*2 = 180 digits.
You have written 189 digits.
Then you wrote another 1994 - 189 = 1805
All the numbers from 100 to 999 have 3 digits
So you wrote 1805/3 = 601 2/3
This means 601 full numbers and 2 digits from the 602. number.
So 100 + 601 - 1 = 700 was the last number you wrote.
Do you agree?