Math Is Fun Forum

Nemexia

Member

Registered: 2015-05-10

Posts: 13

probability

imagine we have 300 different balls possible, at least how many balls should we have so we be sure more than 50% that we have two balls with same color?
i guess the equation would be this (not sure):

300 * C(n,2) * (1/300)^2 * (299/300)^(n-2)   ≥  0.5

and i got answer 19

can anyone solve it?

Last edited by Nemexia (2015-05-10 04:38:20)

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: probability

Hi;

Are there 300 different colors? How are the balls colored?

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

Nemexia

Member

Registered: 2015-05-10

Posts: 13

Re: probability

yes 300 different colors.
original question is:
there can be 300 types of neuron in a nerve, how many neuron should be in a nerve so we be sure more than 50% that we have two neuron with same type in that nerve?

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: probability

Hi;

There are how many of each color?

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

Nemexia

Member

Registered: 2015-05-10

Posts: 13

Re: probability

well, just the type matters, i mean we have infinit amount for each color.

Last edited by Nemexia (2015-07-05 19:36:31)

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: probability

Hi;

I am getting:

which yields an answer of n = 21

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

Nemexia

Member

Registered: 2015-05-10

Posts: 13

Re: probability

Thanks, its correct. Can you please tell me how you found this? Please

Oh i got it thanks!

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: probability

Hi;

Let me know if you need more...

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

Nemexia

Member

Registered: 2015-05-10

Posts: 13

Re: probability

But i can't still solve for n
Any way to do it?

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: probability

Can you do trial and error?

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

Nemexia

Member

Registered: 2015-05-10

Posts: 13

Re: probability

No,

Nemexia

Member

Registered: 2015-05-10

Posts: 13

Re: probability

I mean I shouldn't do that in this problem

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: probability

Do you know that not every equation can be solved by algebraic means? This is one of those.

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

Nemexia

Member

Registered: 2015-05-10

Posts: 13

Re: probability

Oh, OK thanks

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: probability

You might possibly be able to get a decent approximation from an iteration. That would require a computer.

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.