If the numbers after the decimal terminate, yes, it's rational.
9.521521521 = 9,521,521,521 / 1,000,000,000
If they don't terminate, but the pattern continues (which I suspect is the case here), yes, it's still rational.
If <em>x</em> = 9.521521521…, then
1000<em>x</em> = 9521.521521521…
Subtract <em>x</em> from this to eliminate the fractional part:
1000<em>x</em> - <em>x</em> = 9521.521521521… - 9.521521521…
999<em>x</em> = 9512
<em>x</em> = 9512/999
If they don't terminate, but the pattern does <em>not</em> continue, meaning the next few digits could be something random like
9.521521521<u>19484929271283583457</u>…
then the number would be irrational.
