I created a riddle and supplied an answer, I happen to think it is interesting.

As one counts from 1 to 1000000000 how many times does one meet the number nine? An example: from 1 to 100 is 20 because of: 9, 19, 29, 39, 49, 59, 69, 79, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99 and 99 counts as two! So how many times do I meet the number 9 from 1 to 1000000000? You can always count or find a pattern.

Okay the solution is this:

on the interval:

[1,10]=1

[1,100]=20

[1,1000]=300

[1,10000]=4000

[1,100000]=50000

See the pattern! We can in fact prove from [1,10^n] we meet the number nine n*10^(n-1) times. But the proof is ommitted here.

Tell me what you think of it?

Something interesting happens when we count to 10 trillion the number of times we meet 9 is also 10 trillion! Futhermore when the numbers start getting larger than 10 trillion the number of times we meet the nine exceedes the number we count until!