"The hundredth is mine."
Translation:Al o sutălea este al meu.
Think of it as a translation of the one hundredth is mine. In Romanian you cannot skip that one (the o).
OK, I see. So, would this be necessary with miilea, for instance, but not with any of the numbers less than one hundred?
Yes. The one thousandth would be al o mielea. The rule is quite general however. The o accounts for the fact it is one thousand. If it was the two thousandth it would be al două mielea.