Dr. Borg's math lesson du jour, on combinations, is for the benefit of Jazzo and MHR.

What we know:
1. There are 23x23=529 different plants.
2. Breeding a nox fern with a mela grass, and then later breeding a mela grass with a nox fern .. those are the same thing and count only once, not twice (twice would be permutations).
3. Cross breeding means breeding things with other things. Breeding a plant with itself does not count.

So what we want to do is calculate the number of combinations (not permutations) of 529 things taken 2 at a time. The formula for the number of combinations is n!/r!(n-r!) where !=factorial. In our case it would be 529!/2!(529-2)! = 529x528/2 = 139,656.

279,841 would not only include breeding a plant with itself, but would include breeding AxB twice (once as AxB, once as BxA).

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