# Thread: Probability

1. Originally Posted by Daedelus
Wrong. Wrong. Wrong.

If you flip a coin 99 times and get heads every time, what is the probability of you getting tails on the 100th flip?
You are misunderstanding how to use probability with multiple attempts. It's not the individual attempt probablility that is in question. It's the cumulative probablility.

Example: Coin flipping. Pretend Heads = Getting Mount. Tails = Not getting Mount. What is more likely to happen?
A) Getting a Heads in 1 flip
B) Getting a Heads in 5 flips

From your description, the chance of both A and B happening are exactly the same since each indidivudal attempt is a 50% chance.

Well, let's prove what really happens. Try flipping a coin until you get Heads. Repeat that 5000 times. You will see that A happens much less than B. This will happen every single time you do it.

Now, for clarification, this is not a linear relationship. There will never be a 100% chance of getting Heads or Tails. But your chance of "not getting Heads" 100x in a row is low.

2. Originally Posted by voidspark
I advise you to study more probability if you wish to come off as an "expert" but I understand if you give up. It's not for everyone

Here's another justification which could help you "understand" if that is even possible (you don't seem to have a desire to read anything I write): There is a reason I said the next 458 runs, and did not give him credit for the ~40-50 runs he previously did already.

I really love you voidspark, i struggled with this and me and a much more educated friend discussed this, i get it now, after like 50 nights of drinking and arguing about it
(friendly arguing is what we do) .

3. The probability to drop at the x-th try is (1-0.0078)^(x-1) * 0.0078

The propability to drop before(or at) the t-th try is 1-(1-0.0078)^t

The probability to drop after the t-th try is (1-0.0078)^t

The probability to have dropped before(or at) the 77th try is 1-(1-0.0078)^77 which is almost equal to 0.4528=45.28%.

"Expect" it to drop around the 128th try (1/0.0078=128.205128205) but this may vary A LOT!, because the standard deviation is the square root of (1-0.0078)/0.0078^2 which is around 127.7.
You can observe that, if you go down at the very end of the graph page that I have linked bellow and see the Random sample from the distribution section and check the numbers. They are a MESS, they are not near at the "expected" 128! Almost completely random!
Thus, EXPECT NOTHING.

Additional stuff:
http://en.wikipedia.org/wiki/Bernoulli_trial
http://en.wikipedia.org/wiki/Probabi...probability.29
http://en.wikipedia.org/wiki/Geometric_distribution (this is the distribution that our events follow)
Graph(look where it says Plot of CDF at the end of the page): http://www.wolframalpha.com/input/?i...078&lk=4&num=3

4. Just an update guys. Got it a few seconds ago on my 109th run.

5. Originally Posted by Niku
Just an update guys. Got it a few seconds ago on my 109th run.
Which is well around the amount of runs you'd expect to get it in

Grats

6. Originally Posted by voidspark
Which is well around the amount of runs you'd expect to get it in

Grats
Thank you!

7. Originally Posted by Niku
Just an update guys. Got it a few seconds ago on my 109th run.
Grats!
(Well, not that far away from 128 :P)

8. the funny thing is that this thread wasnt needed at all since its explained the on the calculator webpage itself

9. The best part of this thread was watching several people - all saying largely the same thing in essence in most cases - arguing and calling each other wrong because their understanding didn't quite extend to alternate explanations of the same concept.

10. Probability for gamers. No matter how many times you run something, no matter what you do, or how many times you've already done it, the numbers don't change. It will always be less than a 1% chance. Run it 5 times an hour every day till the sun explodes, and it's still a 1% chance to drop. You're committing the gambler's fallacy, basically. Most players do. That's how they keep you hooked. "But I've run it 700 times, it's bound to drop this time." No. No, it's not. It is the exact same 1% drop rate as the first time you ran it. Probability is theoretical, not practical. Besides probability has nothing to do with Blizzard's "fun" RNG.

11. Originally Posted by voidspark
Wowhead frequently seems to reset their data (for instance, when drop-rates change) which means their sample sizes are often not as large as people think. Also with such a low drop rate to begin with, I believe the data is far more error prone (for instance, getting 1 drop versus 2 drops out of hundreds of tries will change the rate a lot!). I'm not great at statistics though, would have to crunch numbers so I can't say for sure if that's right.

- Case in point, if you look at their regular items, you'd think each would have a ~20% drop rate based on logic and the Heroic data (it picks one of 5 items on the table to give you all with equal weight). It seems in the Normal mode data things are a bit fishy with that Leather mantle.
True however in this case it's 1654/212203.

Originally Posted by voidspark
That is definitely not true, I got at least 3 Azure Drakes (don't ask why I ever went back to Malygos).
Yeah but some items work differently to others. It's possible is all I'm saying, unless someone can confirm seeing two.

12. I am describing the chance of him NOT getting it after X consecutive runs. That means that it is still a possibility he will never get it but his chances will be higher to get it THAN not get it after the 619th run (assuming wowhead is right)

#### Posting Permissions

• You may not post new threads
• You may not post replies
• You may not post attachments
• You may not edit your posts
•