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I REALLY need help with this probability equation!

  1. Nov 22, 2012 #1
    Okay, so... I'm not sure this is even the proper place to post this, but I do know this is the proper place to possibly find the answer to this, being that I'm sure there are people who are MUCH BETTER at math than I am....

    So, I play this game, and I've pretty much got everything down, but it's a very very VERY "CHANCE" heavy game.... like, you know, upgrading your equipment starts at 10%, and you can get it boosted up to 50% total, that stuff is easy for me, but then there are OTHER THINGS that have began to confuse me, and I want to know the total number of combinations POSSIBLE for any one item, and then I need someone to figure out the chance of me getting the one combination I'm looking for on a 5 line piece of equipment....

    This is basically how it works...

    Eye accessory
    LUK% 1
    DEX% 2
    INT% 3
    STR% 4
    ALL STATS% 5
    Accuracy 6
    Avoidability 7
    W.DEF (% or number) 8+9
    M.DEF (% or number) 10+11
    Max HP/MP 12+13

    There isn't just 13 values above, there are 26 because I can either get a unique line, or legendary line, and I can only get 5 of these lines, which means I could get luk% dex% str% int% and all stats%, but any of those lines could either be unique lines or legendary lines.

    (Note, unique is 9%, legendary is 12%)

    So it may look like THIS:
    luk 12% or 9%
    dex 9% or 12%
    str 9% or 12%
    int 12% or 9%
    all stats 9% or 12%

    Now here's where the math actually comes in, and this is the part I don't understand...
    I need to know the probability of getting 3 lines of int 12% on a five line piece of equipment...
    SO I want my equipment to look like this(Sort of)

    int 12%
    int 12%
    int 12%

    I know there are 26 values, and I need to go down the line multiplying by the next number like 26*25*24*23 (etc. etc. etc...)

    BUT I don't know how to figure out the PROBABILITY of getting the 3 lines I WANT. Could someone please help a girl out? PLEASE?!?!? :<

    ALSO It would be GREATLY appreciated if you gave me the equations you used to determine the out comes as well, if you wouldn't mind!
  2. jcsd
  3. Nov 22, 2012 #2


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    2017 Award

    Staff: Mentor

    As a good approximation, you can neglect items with 4 or more 12%-int. In that case, you can calculate the probability of (12%int, 12%int, 12%int, something else, something else) in that order - just multiply the individual probabilities. And then you have to multiply the result with 15, as there are 15 possible positions for those 3 12%int-stats.

    In a similar way, you get items with 4 times 12%-int by calculating the probability of (12%int, 12%int, 12%int, 12%int, something else) and a factor of 5 (5 options where "something else" can appear), and items with 5 times 12%-int (no additional factor here).
    Add them, and you are done.

    You might consider 4 times 9%-int as well, as it could be similar to 3 times 12%-int.
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