1) The number of beings has always been, is, and ever will be infinite.
2) Therefore, the beings that are still in ignorance must be infinite.
3) Likewise, the number of beings who have attained Nibbana must also be infinite.
Though it is a rare occurrence indeed that a being anywhere attains Nibbana, yet the number of beings who have attained Nibbana and those who are still in ignorance is equal- both are infinite in number. Or, correctly stated, both are numberless. Just because the number of beings is infinite.
Imagine a line of, say, white marbles along a line of infinite length. The number of marbles would be infinite. Now let us suppose we colour every tenth, or hundredth, or thousandth, or millionth or one in any number, however high, in a different colour, say blue; the number of blue marbles will not be less than the number of white marbles. Just because there is no end to the line, BOTH sets will be infinite in number.
Taking this further, to the limit, it must follow that at any one moment an infinite number of beings attain Arahanthood (while still an infinite number of beings remain in ignorance), an infinite number of Buddhas are preaching the Dhamma on some planet somewhere in Infinity – just because the number of planets where Buddhas appear must also be infinite.
I could go on infinitely, but my time here is finite.