if a opponent opens with 73o utg pre how do we put him on a range?

You assume his raising range is any two.

Yep ... the old 'ATC' (any two cards) opponent can be tough to deal with. So you move on and look at other possible clues that will help you make decisions.

Bet sizing, timing tells, body language

Some ATC players 'can' actually play pretty good poker. You will see drastic changes in their play when 'real' poker decisions are put in front of them ... like 3-betting PF or a c/r spot either way.

If someone is in the gambling mood you just need to tighten up and try to catch a good spot where you can isolate or smash a Flop but just beware that if an ATC Player is contemplating a call/bet that they will probably have 'it'. You want to try and put yourself into 'calling' spots rather than betting spots since then tend to be action junkies and don't like it when someone else is taking their fun (betting) away from them. GL

Easy, his range is 100% at the time he opens. Narrow based on further action.

A player who will play 73o can be very easy to range or very tricky. If he is opening 100% in certain circumstances (for example, if th epot limps to him preflop on the button), then you can include all hands, including 73o, in his range.

The trickier guy is the guy who is playing a normal frequency, say between 12% and 20% VPIP, but will play a polarized range of top 10% hands, ATC to fill out the rest of his opening frequency with bluffs or drawing hands. You are going to have a hard time accurately ranging him.

Any 2 mcgoo. Unless he's a good player doing some insane range balancing, he's a donk. Play him and put him on any 2.

Your opponent may play any two cards preflop, but he probably isn't betting the flop with any two cards.

Just to be clear, you don't try to put him on a specific hand, you put him on a range of hands. If he has a wide range, that sometimes means that he has a lot of hands that are better than yours and a lot hands that are worse than yours in his range. That level of uncertainty makes some players uncomfortable. You have to learn how to operate in that cloud of uncertainty.

anyone consistently opening with those kinda cards UTG is asking for trouble.