Calling all Math Geeks (Chest Drop %)

syntax53
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Joined: Wed Apr 03, 2002 6:00 am

Calling all Math Geeks (Chest Drop %)

Post by syntax53 »

ok, so we can say if you have three 100% chances to "win", then you have a 300% chance overall, because you will win 3 times. however, if you have three 50% chances, you do not have a 150% chance to win. you still have a 50% chance to win, just 3 times. what if you had sixty 50% chances, your overall chance has to be more than 50%.



i'm trying to figure out how i can determine, or at least get as close a possible, your chances at getting an item from a chest. usually a chest will execute 2 or 3 different blocks multiple times. lets use smoking blackwood chest for example ... it executes: random 9060:random 9059:random 9059:random 9059:random 9059:random 9061. now we'll just use a few items for example.



from 9059 we could get a sharktooth trident 9/100 times, a beaded belt 9/100 times, trollskin boots 8/100 times, and an ogre bone bracelet 2/100 times.



now block 9059 is executed 4 times, but we don't have a 36% chance at getting a beaded belt. however, wouldn't the overall chance be greater than 9%?



what if you had a 2/100 chance and a 10/100 chance, would it just be your highest % chance of 10%? or would the only way to show these right we be to say something like "beaded belt (9% x4)" and then even further "diamond (5% x3, 20% x2, 10% x1)" etc?
Raybdbomb
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Joined: Wed Mar 21, 2001 6:00 am

Re: Calling all Math Geeks (Chest Drop %)

Post by Raybdbomb »

ok, so we can say if you have three 100% chances to "win", then you have a 300% chance overall, because you will win 3 times. however, if you have three 50% chances, you do not have a 150% chance to win. you still have a 50% chance to win, just 3 times. what if you had sixty 50% chances, your overall chance has to be more than 50%.



i think you're confusing % of success with chance to "win". for the first case, you'd have a 100% chance now matter how many tries. for a chance of "win" you're looking for what i believe is statistically called the probability density (?). so you have 1.00 (for 100%) x 3 tries = 3 items. 0.50 x 3 tries = 1.5 items on average that you would "win".



i'm trying to figure out how i can determine, or at least get as close a possible, your chances at getting an item from a chest. usually a chest will execute 2 or 3 different blocks multiple times. lets use smoking blackwood chest for example ... it executes: random 9060:random 9059:random 9059:random 9059:random 9059:random 9061. now we'll just use a few items for example.



from 9059 we could get a sharktooth trident 9/100 times, a beaded belt 9/100 times, trollskin boots 8/100 times, and an ogre bone bracelet 2/100 times.



now block 9059 is executed 4 times, but we don't have a 36% chance at getting a beaded belt. however, wouldn't the overall chance be greater than 9%?



technically i believe you should have a 36% chance of getting a beaded belt. this is true because 0.09 x 4 tries = 0.36 items "won", AKA 36% chance of getting it



what if you had a 2/100 chance and a 10/100 chance, would it just be your highest % chance of 10%? or would the only way to show these right we be to say something like "beaded belt (9% x4)" and then even further "diamond (5% x3, 20% x2, 10% x1)" etc?



i think you're saying "what if you had a 2/100 chance and a 10/100 chance of getting the same item". if that is true, you would have a 12% chance because 0.02 x 1 try + 0.10 x 1 try = 0.12 items "won"
syntax53
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Joined: Wed Apr 03, 2002 6:00 am

Re: Calling all Math Geeks (Chest Drop %)

Post by syntax53 »

i think you're confusing % of success with chance to "win". for the first case, you'd have a 100% chance now matter how many tries. for a chance of "win" you're looking for what i believe is statistically called the probability density (?). so you have 1.00 (for 100%) x 3 tries = 3 items. 0.50 x 3 tries = 1.5 items on average that you would "win".

i was just using "win" as an example of "winning the item" or "winning the lottery." the first example was assuming there was only 1 item to be won/gotten. the problem with saying "0.5 * 3 = 1.5 items won" is because i'm not interested in how many items i win, i want to know the chance of winning those items.



technically i believe you should have a 36% chance of getting a beaded belt. this is true because 0.09 x 4 tries = 0.36 items "won", AKA 36% chance of getting it

this isn't true because if it were just two items at 50%, then .5 * 2 = 1.0 (or 100% chance). that's false.



i think you're saying "what if you had a 2/100 chance and a 10/100 chance of getting the same item". if that is true, you would have a 12% chance because 0.02 x 1 try + 0.10 x 1 try = 0.12 items "won"

again, what if it were a 90% chance and a 10% chance. (.9 * 1) + (.1 * 1) = 1.0. you don't have a 100% chance.
Raybdbomb
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Re: Calling all Math Geeks (Chest Drop %)

Post by Raybdbomb »

yea but if you divide items "won", or how many items you get divided by the tries, you get the effective percentage of getting BOTH. but i guess you're looking for the probability that you get either of the items? if there are 2 items and each gives a 50% probability, then there is 25% probability you will get neither, 50% probability you will get one of them and 25% probability you will get both of them. i believe this can be calculated with a probability tree, with independent results. chuck is getting a master's in probability, how about a little input from him?



but i think you're saying that there is only one item, and there is a 50% chance applied twice that you will get it (for example). this would be dependent, which can still be calculated with a probability tree, but a different one
syntax53
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Re: Calling all Math Geeks (Chest Drop %)

Post by syntax53 »

yea but if you divide items "won", or how many items you get divided by the tries, you get the effective percentage.

using this formula with my example of 1 item at 50% with sixty tries, 0.5*60=30 items won on average... 30/60 tries = 0.5 effective percentage or 50%. the second calculation is the opposite of the first.

i believe this can be calculated with a probability tree, with independent results. chuck is getting a master's in probability, how about a little input from him?



lemme formulate a reply and i'll get it out

i agree, i just dont think it's as simple as what has been suggested.
Raybdbomb
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Re: Calling all Math Geeks (Chest Drop %)

Post by Raybdbomb »

sorry, i edited it after that, you weren't supposed to read it yet :P



but then i contradicted myself...

:wstupid:
Scruff

Re: Calling all Math Geeks (Chest Drop %)

Post by Scruff »

using this formula with my example of 1 item at 50% with sixty tries, 0.5*60=30 items won on average... 30/60 tries = 0.5 effective percentage or 50%. the second calculation is the opposite of the first.



The only problem with that conclusion is that percentages in mmud are not cumulative. On a 50% chance, with 60 tries, there is a possiblity to get the item 60 times or 0 times because EVERY try the % resets itself. Granted, on average the number of items will fall around 50% (usually +/- 15% or so with that small a sample size). Like Ray said, the best way is with a tree because probability is really what you're interested in.



edit: damned typos
Raybdbomb
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Re: Calling all Math Geeks (Chest Drop %)

Post by Raybdbomb »

but a standard tree does not really account for a limited number of items...



if you get 60 shots at a lim1 item that drops 50%, the probability would be like .99995 that you would get it. i guess you could get that through a tree, but it'd be a damn ugly tree, more like a big diagonal



edit, probability would be 1-(0.50)^60 actually, which is 0.9999999999999999991326382620116
Sven
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Re: Calling all Math Geeks (Chest Drop %)

Post by Sven »

uh, this is statistics guys. They actually have formulas for this. I'll look in my notes and post it, and you guys can have fun figuring out wtf it all means. :)



Basically, you need to figure out how many "items" you want to win. If you want to know your chance of winning atleast 1 item, then you have a very high %. If its win ALL of them, then you have a very low percent. So, have to figure out what you want.
EvanElias
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Joined: Mon Jul 05, 2010 12:42 am

Re: Calling all Math Geeks (Chest Drop %)

Post by EvanElias »

yeah, if you define very carefully what specific probability you're trying to find, this'll be a lot easier to answer :)



In answer to your first question in the initial post, the chance of getting a beaded belt is 1 - (.91 ^ 4)... which is the inverse prob of the chance of not getting a belt in 4 trials...



some prob/stats experience is helpful here, a lot of prob results are somewhat counter-intuitive.
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