Problem with my ball bag...

[Burty88]

...Can any mathsy people out there just confirm I got a question right on a stats paper I just took?

A bag contains 5 white balls, 2 blue balls and 5 red balls, the balls are taken from the bag in succession without being replaced.

Q. What is the probability that the second ball is red?

I got (5/12 * 4/11) + (7/12 * 5/11) = 5/12

Thanks in advance,

[RemaL]

not what I was expecting

[Silverbullet767]

This is not what I was expecting this thread to be about....

I think the answer is. Wednesday.

[Project 644]

A Blue Whale?

[Gun]

You really do have a problem with your ball bag if you've got all that in there.

[zakelwe]

Why does it mention 2 blue balls in the bag? Shirely that is irrelevant?

Andy

Edited by zakelwe on Tuesday 12th January 11:32

[Kit80]

I hope this get moves to health matters

[ccr32]

you've got herpes.

[tribbles]

I think it's the probability that you have 2 red, or 1 non-red followed by a red:

(2/12 * 1/11) + (10/12 * 2/11)

= 2/132 + 20/132
= 22/132
= 2/12

= 1/6.

[louiebaby]

I get 15/44.

Which is .34 or 34%.

I look forward to the answer.

[Stupidlikeafox]

42.

[robinhood21]

Pain. Lots of it!

[Burty88]

tribbles said:

I think it's the probability that you have 2 red, or 1 non-red followed by a red:

(2/12 * 1/11) + (10/12 * 2/11)

= 2/132 + 20/132
= 22/132
= 2/12

= 1/6.

But there's 5 red balls in my ball bag, so would it not be the same equation I got?:

(5/12 * 4/11) + (7/12 * 5/11)

[Incorrigible]

Burty88 said:

tribbles said:

I think it's the probability that you have 2 red, or 1 non-red followed by a red:

(2/12 * 1/11) + (10/12 * 2/11)

= 2/132 + 20/132
= 22/132
= 2/12

= 1/6.

But there's 5 red balls in my ball bag, so would it not be the same equation I got?:

(5/12 * 4/11) + (7/12 * 5/11)

No, there's either 5 red or 4 red after then first one's taken out

I think Tribbles is right

[tribbles]

Incorrigible said:

Burty88 said:

tribbles said:

I think it's the probability that you have 2 red, or 1 non-red followed by a red:

(2/12 * 1/11) + (10/12 * 2/11)

= 2/132 + 20/132
= 22/132
= 2/12

= 1/6.

But there's 5 red balls in my ball bag, so would it not be the same equation I got?:

(5/12 * 4/11) + (7/12 * 5/11)

No, there's either 5 red or 4 red after then first one's taken out

I think Tribbles is right

I'm wrong - I misread the colour ordering.

5 white, 2 blue, 5 red

(I read it as 5 white, 2 red, 5 blue).

ETA: Just put in the right numbers:

(5/12 * 4/11) + (7/12 * 5/11)

Which does indeed make 5/12.

Edited by tribbles on Tuesday 12th January 11:45

[Devilstreak]

God this takes me back, Not that I can remember any of it though

[Burty88]

Incorrigible said:

Burty88 said:

tribbles said:

I think it's the probability that you have 2 red, or 1 non-red followed by a red:

(2/12 * 1/11) + (10/12 * 2/11)

= 2/132 + 20/132
= 22/132
= 2/12

= 1/6.

But there's 5 red balls in my ball bag, so would it not be the same equation I got?:

(5/12 * 4/11) + (7/12 * 5/11)

No, there's either 5 red or 4 red after then first one's taken out

I think Tribbles is right

I'm not disagreeing with his method, mine's the same. It's just that his equation relies on the assumption that there's two red balls and 10 non red balls when actually there's 5 red and 7 non red. After the first draw of ball there's either 5 red balls or 4 red balls left and 6 or 7 non reds respectively.

[louiebaby]

louiebaby said:

I get 15/44.

Which is .34 or 34%.

I look forward to the answer.

It's the number of red balls in the bag after one round, divided by 11.

Therefore there is a 5/12 chance of there being 4 red balls after the first turn, and a 7/12 chance of there being 5 red balls after the first turn. There are therefore 55/12 red balls in the bag after the first round. 55/12 /11 = 55/132 = 5/12.

My original answer was wrong, as I'm a wally.

[V8mate]

Green.

[plasticpig]

Not enough information to answer the question. Are the balls all the same size? Can the person removing the balls see the balls in the bag? If so what is the persons favourite color.....