This is the well known Monty Hall problem. U can't work out...

This is the well known Monty Hall problem. U can't work out whether to switch or not unless you think U can read the other person's mind.
For mine, you now have a simple random choice between the two boxes; I'd pretend to be puzzling over the choice (to kid Monty and audience along), then pick at random either the one I picked b4 or the other left ... fifty fifty chance IMO.