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#1 2018-03-29 13:12:24

Hannibal lecter
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Registered: 2016-02-11
Posts: 225
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very real important question about probability ..

when you toss a coin three times, Let x denote the number of heads that appear
find p(x)?

!!!!

is there a general law for this question? how to find this probability?
it's really harddddddddd

Wisdom is a tree which grows in the heart and fruits on the tongue

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#2 2018-03-30 07:51:49

bob bundy
Registered: 2010-06-20
Posts: 8,462

Re: very real important question about probability ..

Well x can be 0 1 2 or 3, so is this asking for P(0), P(1), P(2), and P(3) ?

Bob

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob Bundy

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#3 2018-03-30 10:59:39

Hannibal lecter
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Registered: 2016-02-11
Posts: 225
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Re: very real important question about probability ..

yes but He is asking for a general rule!
is there a general rule for that?

Wisdom is a tree which grows in the heart and fruits on the tongue

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#4 2018-03-30 11:02:38

Hannibal lecter
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Registered: 2016-02-11
Posts: 225
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Re: very real important question about probability ..

this is the full question in the following image :
and please give me the full answer for all the questions a b and c, because I have an exam please! just this time

Last edited by Hannibal lecter (2018-03-30 14:11:32)

Wisdom is a tree which grows in the heart and fruits on the tongue

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#5 2018-03-30 21:44:48

bob bundy
Registered: 2010-06-20
Posts: 8,462

Re: very real important question about probability ..

Ok, I understand.

When you throw a coin it could be heads or tails, each with P = 1/2

So if you want (let's say) two heads that means also one tail so multiply the probabilities to get 1/2 x 1/2 x 1/2.

But this doesn't take account of the order: hht, hth, or thh.  So in this case we calculate like this:

3 x (1/2) x (1/2) x (1/2)

The formula for "r" heads is

nCr x (1/2)power r x (1/2) power(n-r)

The sum of these for all values of r, is 1, which makes it a probability mass function.

Note no up arrow on my Kindle, so I've used the word power.

Bob

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob Bundy

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#6 2018-03-30 23:51:32

Hannibal lecter
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Registered: 2016-02-11
Posts: 225
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Re: very real important question about probability ..

nCr x (1/2)power r x (1/2) power(n-r)

can you write down this rule again more clearly please,
I can't not understand what is x (1/2)power r please.. my exam is tomorrow
is x a variable or multiplication symbol,
please I won't ask too much again, but the formula is not clear can you type it clearly or like image or anything...
and what will be n value and the k value ?

Last edited by Hannibal lecter (2018-03-31 01:06:37)

Wisdom is a tree which grows in the heart and fruits on the tongue

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#7 2018-03-31 01:25:43

bob bundy
Registered: 2010-06-20
Posts: 8,462

Re: very real important question about probability ..

I am typing on a Kindle to give the quickest response but the keyboard options are limited.  There's an excellent page here:

www.mathsisfun/data/binomial-distribution.html

Bob

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob Bundy

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#8 2018-03-31 02:52:01

Hannibal lecter
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Registered: 2016-02-11
Posts: 225
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Re: very real important question about probability ..

I'll see that after few hours, but

do the formula you provide mean like that following picture,
( please look at it, is is the same as you wrote)

Wisdom is a tree which grows in the heart and fruits on the tongue

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#9 2018-03-31 04:54:31

bob bundy
Registered: 2010-06-20
Posts: 8,462

Re: very real important question about probability ..

Yes, that's it exactly. I cannot implement square bracket codes at the moment.

Bob

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob Bundy

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#10 2018-03-31 07:51:51

Hannibal lecter
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Registered: 2016-02-11
Posts: 225
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Re: very real important question about probability ..

is n = 3 or r = 3 ? if the coin tossed 3 times , or it's not either

Wisdom is a tree which grows in the heart and fruits on the tongue

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#11 2018-03-31 19:51:35

bob bundy
Registered: 2010-06-20
Posts: 8,462

Re: very real important question about probability ..

n is the number of coins and r the number of heads.

Bob

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob Bundy

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