kittenbalm
a jar contains 4 green marbles, 5 red marbles, and 7 blue marbles. If two balls are selected randomly what is the probability of getting :
1. 1 green and 1 blue
2. 2 red
3. 1 blue and 1 red
4. 2 blue
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kittenbalm
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hey help please?
yrelhan4
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well i just got confused.. give me a minute.
kittenbalm
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okay the title of lesson is combinations i got no idea how to do it lol
kittenbalm
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@ganeshie8
Zarkon
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are you sampling with or without replacement?
kittenbalm
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without i think
Zarkon
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then this is a hypergeometric distribution
kittenbalm
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a what????? lol explain
Zarkon
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suppose you have a box with a red and b green balls. you grab k balls
the prob you get r red and g green balls (r+g=k) is given by
\[\frac{ _aC_r _bC_g}{_{(a+b)}C_k}\]
kittenbalm
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yeah i dont get it
Zarkon
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\[\frac{_aC_r\cdot_b C_g}{_{a+b}C_k}\]
Zarkon
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do you know what \[_nC_r\] is ?
kittenbalm
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not at all
Zarkon
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\[{n\choose r}\]?
kittenbalm
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nope
i dont know any of this stuff
Zarkon
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permutations/combinations?
yrelhan4
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i think it would be easier if we dont use combinations, zarkon..
it would be easier if if we do it like this..
for 1 green ball. 4/16..
1 blue ball after 1 green ball hass been selected.. 7/15. and then multiply them..
whats your view?
kittenbalm
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i knwo thats what this unit is called combinations
yrelhan4
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eh right. so it would be like 4/16*7/15 + 7/16*4/15.. right?
kittenbalm
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id think s if that was the case
kittenbalm
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wait but youd get the same thing right
7/60 + 7/60
yrelhan4
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yup.
yrelhan4
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then for the second part.. 5/16*4/15..
you get why?
kittenbalm
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which would equal 14/60 right because you dont change the denominator right or would it be 14/120
yrelhan4
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yeah.
kittenbalm
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so it is 14/120
yrelhan4
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am i right with the second part @RolyPoly ?
yrelhan4
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it should be 14/120..
Zarkon
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no
yrelhan4
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14/60.. lol
Zarkon
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the answer is 7/30
kittenbalm
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well
idk how to do this thn i am so lost im gonna fail lol
Zarkon
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or 14/60 if you like
kittenbalm
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how
Zarkon
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the solution is written above
kittenbalm
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okay so will you help by showing work on two three and four maybe if i see it on three ill be able to do it
RolyPoly
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P(blue first, then green)
= P(blue) x P(green after drawing a blue)
= 7/16 x 4/(16-1)
= a
P(green first, then blue)
= P(green) x P(blue after drawing a green)
= 4/16 x 7/(16-1)
= b
P(1 blue and 1 green)
=P(blue first, then green) + P(green first, then blue)
= a + b
kittenbalm
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now im deffinately confused i just ned a simple explanation
RolyPoly
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2 red, similar, despite the order of picking a red doesn't matter this time, since you don't the red ones are identical
kittenbalm
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what omg i need a tutor
RolyPoly
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Which part are you confused at?
kbrece1
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2 BLUE
kittenbalm
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2 red actually all of it really
kittenbalm
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u gonna help k?
kittenbalm
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no thats not the question
@phi help please