I'm perplexed in front of the following questions. I hope I get clear explanation for it...
A box of biscuits contains 9 diff. varieties (e.g. A, B, C, D, E, F, G, H, I). In how many ways can 4 biscuits be chosen if: Two each of two varieties are selected?
The final answer is 36 but I don't how to get this answer as I don't understand exactly what does it mean "Two each of two varieties are selected" and I'd love to see several examples for it using the letters (no need to list all the 36 combinations of course - just a couple will be fine for me get the hang of the question). For example: is it something like (AB)(AB)? or (AB)(CD)? or what?