[5NL] AJo on button, 2P on paired flop.

I thought there was a thread on the topic I can't find it at the moment you can look for it yourself.

A quick rundown on counting combos.

There are 6 combos of each pair since you have 4 cards to choose from. 4c2(Read 4 choose 2). AB AC AD BC BD and CD. AB=BA since order doesn't matter so AsAh is equivalent to AhAs.

There are 16 combos of every other hand with 4 of those being suited. We have 4 cards to choose from then 4 again so 4*4 gives us 16 combos or 4c1*4c1.
Note: 4 of these are suited.

There are 52c2=1326 combinations of hand

Now once we see the flop both our range and opponents range becomes more limited. If villains range is AA and 22 he has 12 combos of hands. Once the flop comes A44 he only has (3c2)3 combos of AA and 6 combos of 22 now. If the flop came AA4 he would only have (2c2)1 combo of AA.

For non pair hands we can simply multiply as follows. If our villain has AK and the flop is Axx he now only has 12 combos(3*4) of AK. AKx flop he has 9combos(3*3). AAK flop he only has 6 combos(2*3). If we have AK and the flop is AAK our villain only has 2 combos(1*2).

If you need more explaining I can make a better, less rushed post. This should be enough to get you started on thinking about counting hand combinations though.

Note: 52c2 means 52 choose 2 which is basically 52*51 / 2*1.
It's really (n)! / k!(n-k)! where n is 52, k is 2.