Tough Probability (1 Viewer)

[LaCe]

I had this question in my 3u half yearly, and i did a question just like it before!!! But i cant remember how i did it, so here's the question from the exam:

A bag contains 6 black and 4 white marbles.

From the original bag of ten marbles, 3 are drawn at the one time. Thses 3 are put into another bag and one marble is drwn without looking. What is the probability that this marble is white?

In the question, is there a different between if u take one at a time and all at one time? I dont think there is but...?

Well I found the probability of getting 3W, 2W/1B and 1W/2B.
Then i multiplied each of those by the probabilty of drawing a white from each.
Is this correct?
i cant remeber the answer, something with a five in it...haha
Thanks

 

[FinalFantasy]

ahh dey should take probability out of the syllabus!!

 

[LaCe]

ahh dey should take probability out of the syllabus!!

Yeah i know! Prob is a bitch

 

[Pace_T]

From the original bag of ten marbles, 3 are drawn at the one time. Thses 3 are put into another bag and one marble is drwn without looking. What is the probability that this marble is white?



6c0.4c3/10c3 * 3/3
+
6c1.4c2/10c3 * 2/3
+
6c2.4c2/10c3 * 1/3

i think that is it

1/30 + 1/5 + 1/4
=29/60

 

[LaCe]

FUCK! I was sooo close

 

[Slidey]

ahh dey should take probability out of the syllabus!!

No way hosey!

 

[Pace_T]

lol you mean jose
ahhaaha

 

[Slidey]

No, I mean hosey. Variations.

 

[LaCe]

Actually i got the right answer in the exam.

Its this:
WWW: 4/10*3/9*2/8*1
WWB: 4/10*3/9*6/8*3*2/3
WBB: 4/10*6/9*5/8*3*1/3

WWW+WWB+WBB=2/5

And that s how easy it is, i cant believe i got it right!

 

[FinalFantasy]

lol, i hope i can pull myself together and level up some probability some day before the HSC......

 

[LaCe]

I know im not that great with prob but i cant believe i pulled that off, i just multiplied by 3 for some reason, cause i thought it looked right and cause i thought that was the way to arrange them whhich was right! 4u Maths exam on wednesday, permus/combos in it, hopefully i can pull something out of my arse for that one

 

[FinalFantasy]

wow, a 4u maths exam on combo\perm.....
i would b dead if i had to do it LoL!

 

[Pace_T]

omg man i am soooo sorry
see in my answer, in the last line of working out

instead of
6c2.4c2/10c3 * 1/3
it is
6c2.4c1/10c3 * 1/3

then
6c0.4c3/10c3 * 3/3
+
6c1.4c2/10c3 * 2/3
+
6c2.4c1/10c3 * 1/3


1/30 + 1/5 + 1/6
=2/5

just a simple typo that i had used in the calculation. so there is another method to doing it. (probably a more correct way since it is using C )

sorry for the confusion dude, i can only imagine how many marks that was worth and how pissed off you would have gotten when seeing a different result and no one disagreeing with my one ...unless if u already saw that mistake lol.

Thanks,
Pace T.

 

[Pace_T]

I wish you the best of luck for your 4 unit exam with permutations and combinations in it
LOL!

 

[LaCe]

THanks man, had it, and there weren't any permus/combos but everything else was hard. Q7, q8 style questions from past trial exams, etc... Hardest shit ive ever seen but it was cool, everyone else fucked up so its all good