probability

danman111177 · 2011-03-03 23:30:41

what is the probability of geting a desired result from a number of attempts.

An example would be 3 x a result of 5 or 6 when you roll 5 dice. So you roll 5 dice and you want to get 3 results of 5 or 6.

Hope I made that clear.

Danny

bobbym · 2011-03-03 23:34:21

Hi danman111177;

Welcome to the forum! I am not sure what you require. Do you mean 5,5,5 or 6,6,6?

danman111177 · 2011-03-04 08:45:16

thanks. You have five dice. both a 5 or a 6 gives a positive result. I want 3 positive results.

bobbym · 2011-03-04 09:49:33

Hi;

That means (5,5,6), (5,5,5),(6,6,6),(5,6,5),(6,5,6) etc.?

If so the answer is:

danman111177 · 2011-03-04 20:50:43

Thanks for that, but 2 things

1 just to make sure this is 3 positive results from 5 dice

2 its the formula I wanted as the example is just hypothetical.

cheers

bobbym · 2011-03-04 21:06:34

Hi;

Yes, this is exactly 3 positive results, provided that this is what you call a positive result:

(5,5,6), (5,5,5),(6,6,6),(5,6,5),(6,5,6),(6,5,5) etc.

The P(5 or a 6) is 1 / 3 so p = 1 / 3. n = 5.

danman111177 · 2011-04-04 12:16:44

sorry to be a pest but that just isn't working out for me.

the fraction I get it 20/729. I'm assuming the first brackets is a fraction (which is where Imust be going wrong) and not something I vaguely remember from school. If so what is it so I can look it up.

But yes this appears to be the formula I want.

thanks for help

edit - ok yup I now remember matrices but still working on how that gets to a fraction

edot - figured it out - thanks very much

Last edited by danman111177 (2011-04-04 12:34:31)

danman111177 · 2011-04-04 12:45:17

ok so now have a new problem if you'll bare with me - what the probability of getting at least 3 positive results?

bobbym · 2011-04-04 12:52:02

Hi;

Please, one question at a time. You are still not clear on your first question.

danman111177 wrote:

I'm assuming the first brackets is a fraction

That first bracket is not a matrix or a fraction. It is read 5 choose 3. It is the number of ways to choose or select 3 objects from a group of 5. Its numerical value here is:

Now for your new question.

danman111177 wrote:

what the probability of getting at least 3 positive results?

This is the formula.

So with n =3 and p = 1 / 3. The probability of getting 3 or more positive results in 5 throws of a die is:

danman111177 · 2011-04-04 18:29:15

thank you very much. never would have solved it on my own.

bobbym · 2011-04-04 23:09:46

Hi danman111177;

Your welcome.

never would have solved it on my own.

Everybody says that but it is just not true. If you do enough of these you will start getting some of them. See you later.

Math Is Fun Forum

#1 2011-03-03 23:30:41

probability

#2 2011-03-03 23:34:21

Re: probability

#3 2011-03-04 08:45:16

Re: probability

#4 2011-03-04 09:49:33

Re: probability

#5 2011-03-04 20:50:43

Re: probability

#6 2011-03-04 21:06:34

Re: probability

#7 2011-04-04 12:16:44

Re: probability

#8 2011-04-04 12:45:17

Re: probability

#9 2011-04-04 12:52:02

Re: probability

#10 2011-04-04 18:29:15

Re: probability

#11 2011-04-04 23:09:46

Re: probability

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