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If by completion you mean successfully getting out of the room on time, then it mostly depends on which room you play in first. I played two games and successfully got out both times. Ask the employee for the easiest room first and then increase the difficulty.
There is a completion percentage as well as difficulty level posted on their website for each room. Each room will vary in these percentages.
You can look up the different scenarios on their website. Each one is given a list of stats including the completion rate. Usually the difficulty and the completion rate go hand in hand.
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