Combinations/Permutations

Factual Questions
1

I want to calculate the number of combinations possible by pairing two items of different types.

For instance: letter/number pairs. If counting actual pairs without regard for order (A3 and 3A are the same pair and NOT counted twice) Is the formula:

of letters multiplied by # of numbers = possible pairs?

Just double checking my assumption…

2

Yes.

(Imagine putting the pairs into a rectangle, whose columns correspond to letters and whose rows correspond to numbers. You can count the number of cells by multiplying the number of columns by the number of rows)

3

The multiplication counting principle says that if there are A ways to make the first choice and B ways to make the second (and C ways…), then the combos are AxB(xC…).

You’ve got A letters and B numbers, so it’s AxB.