For reasons of transfinite cardinal addition and multiplication, the ratio of an infinite cardinal C to itself is much akin to the ratio 0/0. E.g., since one can take all the naturals N and subtract all the even numbers from N so as to represent a case of N - N, but one still has N-many numbers left over (the odds), then N/N = 1 is possible, as is such as = 2, and = 3, and so on. And by multiplicative inversion can this be checked: if N/N = 2, then 2 times N = N, which is also true of the cardinality, here. This is because |N| + |N| = |N|, then.
Moreover, since N times N = N (assuming the axiom of choice, at least, as far as I know...), then there is a way for N/N = N too.
The ratio of N to R would be like an infinitesimal, since N is infinitely smaller than R (much smaller, we often imagine).
The ratio N/n would evaluate to N. Suppose N/2 = N. This means that subtracting 2 from N that many times could yet mean N-many more left over (due to above kinds of reasons). Or, again, N by 2 = N, "and we are almost done."
"Basically," in the sphere of infinite sets, the theory of probability has to be adjusted accordingly. You might very well find out that, other things being equal, the number of worlds with life-supporting constants was equivalent in size to the number of worlds with life-blocking constants. (This perhaps only insofar as talk of the constants varying "just like that" is realizable in the first place: there could be something about all possible worlds such that their physical constants all have to be a very specific way, even if we thought there was some meta-possibility of the constants differing.)
There is, however, a relation of "almost all" or "all but finitely many," i.e. the cofinitude relation, that, if it held in this kind of case, would open the door to the number of life-supporting worlds to be finite in number, even out of infinitely many possible worlds. I.e. we would have to claim that all but finitely many worlds are lifeless, which would be a great deal to insist upon with almost entirely a priori reasoning as one's only serious justification for making such a claim.