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BGonline.org Forums
SOLUTION
Posted By: Bob Koca In Response To: SOLUTION (Timothy Chow)
Date: Wednesday, 10 January 2024, at 4:38 a.m.
Here are the two ways I did it:
A) Roll until you get an odd number or a 6. Since those are 2/3 of the rolls it takes 3/2 turns on average for that to happen. 1/4 of the time you got a 6 and the game is over and 3/4 of the time you have a restart.
So we have the equation E = (1/4)(3/2) + (3/4)E. Solving gives E = 3/2.
B) I suspect this may be really the same as your explanation but I think it is a bit nicer:
Generate the list of random numbers backwards. When you get to a 6 it will take 3/2 rolls on average to get another 6 or an odd number. That number of rolls is how long it took to get the 6 looking at it forwards with the odd numbers resetting the count.
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