not fail more than 4...more in last 5 rooms is be very lucky... mmm i dont know yet how know the number averange of tryes but if without increase the number is 6 really doubt that will go down to 4..cause well ....chance only increase a little in that 4 try....so well even if reduce a little the averange i think 5 is the best answer we could get that means if you get below 5 always you are very lucky....and is averange...you could in theory fail all 15 tries in a row ...you cant fail 16 cause then all is correct....