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An urn contains 7 white balls and 3 red balls. Three balls are selected. In how many ways can the 3 balls be drawn from the total of 10 balls
a) If 2 balls are red?
b) If 3 balls are red and 2 are white?
c) If at leas 4 are red balls?
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I'm trying to understand the problem.
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I suppose I have to use combinations.
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me too
are we taking out 3 or more?
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it says 3 but then talks about if 4 are red...
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three
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so for the first are we assuming that 2 of the 3 we are taking out are red or...?
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I guess. But if that is the case then I need to use a permutation.
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that's what I'm confused on
if the first question is asking 'we draw 3 balls, how many ways can we do this of two of the three we take out are red?'
then I would say
3 ways to select red balls
7 ways to select the white ball
3*7=21
but then what about the rest?
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that's if the balls are unique of course^
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No they are not unique.
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oh, well then I'm really confused.
I especially don't see how you can have 4 red balls when it says there are 3 in the urn..:/
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Ahhh!
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I made a mistake. I copy part of the problem below the one i wanted.
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that makes sense
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b) If all 3 balls are white.
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c) If all 3 balls are red=
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Sorry =/
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well I still don't get the question. if it is as I said above and the balls are not unique, then...no I'm lost, sorry
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Well at least I'm don't feel alone with the problem =)
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I really want to understand this counting techniques.
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lol
I'll be interested to see if someone understands it.
Buena suerte!
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Thank you!
notsmart
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mindception
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I think you were right TuringTest. They can be called: red_1, red_2, red_3, etc.
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In that case I'm selecting 2 out of 7 white balls and 1 out of 3 red balls. So.
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\[C(7,2)\cdot C(3,1)\]
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I though the first was 2 red balls and one white
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does the order that we pull them out in matter?
I guess it should, so my above answer is wrong.
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Sorry my bad.
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a) If2 balls are white and 1 is red.
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The order matters, otherwise I'm lost.
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yes, otherwise the answer to c) is 1
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exactly!
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Tu sabes español verdad T
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well c) should still be the easiest:
3!=6
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on poco
tengo que hacer la tarea para miercoles. no hice nada en lalas vacaciones!
estas de acuerdo conmigo acerca parte c) ?
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un*
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Ahh. What do you think about this: I help you with your spanish, and you can help me with my english.
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What homework?
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your english is a lot better than my spanish
I'm going to school here taking language classes
do you agree about part c?
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I think the answer to c) is 1
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only if the order doesn't matter
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if it does then it is 6
do you want me to convince you?
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Are you sure the order matters?
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no
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Me neither.
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lol
oh man...
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I'm going to draw some circles to represent the balls lol
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me to I guess
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Well Hero sometimes help with my english. Hi write something to him and he says: "No, you can write that in this way". I'm very grateful to him, but I'm ashamed that I can't not help him with something I know.
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I was wondering if I can ask you similar things, and I can help you if you have spanish doubts.
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Well even if you can't help me, you can always ask me if you have some doubts.
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"can't not help him"
should be
"can't help him"
and I your the first mexican I've met who actually wants to help. All my friends just make fun of me.
anyhow
I see 6! ways te select 2 white balls out of 7
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thanks by the way
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I meant 6+5+4+3+2+1=21 ways to select the two white ones
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But if the order matters It should be a permutation, so P(7,2) is not equal to 6! I think.
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no, I was wrong about that sorry
my working theory is that the order does not matter and that there are 21 ways to select 2 white balls out of seven, and 3 ways to select the red one for each of those, so
21*3=63 ways for part a)
make any sense?
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Yes! that makes sense!
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ok then let's see if I have anything for b)...
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I thought about selecting 3 whites out of 7, so C(7,3) = 35
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I agree :D
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well so then the answer is
a)63
b)35
c)1
IF the order of selection does not matter.
so what if it does???
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Mmm good question, I'm thinking about it.
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I don't think I know how to do those.
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So you think this problem is done?
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That would be great! hehe
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I think you probably know better. Where did you get this problem? Does it seem like it should be so difficult as to have to consider order?
That seems extraneous to me, unless you have an advanced combinatorics book or something.
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It is from the book: "College Algebra" written by Sullivan. It seems isa High School book.
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Then I think we are done :)
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Thank you =). And what do you have to do for homework?
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I'm trying to figure out what my girlfriend just texted me...
chulos ojos de perrito enamorado
not sure what enamorado means, but it must be enamored, eh?
I have to do adverbs, practice past participle, negations, and... I don't know. A lot. I should have done it over break.
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Are you in school?
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enamorado means to be in love.
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awww
well that's almost what enamored means
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I finished my credits at college, I hope to get my undergraduated grade this year.
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in what subject?
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Mechatronics Engineering
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I don't understand quite well what you mean with enamored. Does that word exist in english?
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Dang, what math did you have to take for that?
I would think a lot, but it seems like you don't know too much more than me.
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enamored means obsessed basically, but the word doesn't mean something quite as bad as obsessed
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Ahh so you were almost right.
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or 'awestruck'
like I'm enamored by the presence of somebody special
so almost...
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well I took the basics matehmatics, Algebra, Linear Algebra, Analytic Geometry, Calculus, Probability(Even it seems I didn't), Differential Equations, Complex Analisys, etc.
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Cool!
at UNAM ?
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yes, How did you know?
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because that's where I want to go
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and you told me you lived in DF
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Ohh, want do you want to study there?
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What, sorry.
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Whatever the highest physics I can get into is.
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what sorry???
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I mispelled something, nevermind. So you want a physic's PhD, at UNAM.
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If I can. I don't know how they feel about gringos getting in though.
But UGDL sucks.
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So you are studying at UGDL right now.
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Why sucks?
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Just two classes. Between that, moving here, and language I'm busy.
It's just a bad system in my opinion. They don't have high enough standards.
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You mean academic standars, or administrative standars?
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academic was what I meant, but I'm sure administrative as well. My girlfriend had 4/6 of her graphic design teachers be about 25 years old. I'm almost that old! Not exactly tenure...
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Well the teachers here are very old hehe.
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but there is a good academic level too.
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But I think that the best option is at Cinvestav, have you heard of it?
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no, where's that?
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It's has several (places?) on the country, Queretaro, D.F, I'm not sure if Guadalajara.
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I'll look into it. wrote the name down
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There you can find the best academic level in the country.It is difficult to get in.
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CINVESTAV
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brief english lesson:
It's has several (places?) on the country
It has several locations in the country
^^^correct
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Ohh thank you, that is what i meant with my bad english!
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There is a Guadalajara's Cinvestav.
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I wish you could just give me little tips like that in spanish, but I've only been taking classes for 2 1/2 months.
It'll be awhile befor I'm fluent :(
-there is?!?!?
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Don't worry feel free to write in spanish. That is the best way to learn, by practicing
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(there is is wrong?)
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Thanks for not laughing at me... or at least thanks for not writing lol!!
what 'there is'? where
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oh mine
that was to your last comment about there being a school here
I went 'there is?"
out of surprise
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Don't worry =P. I was telling you that there is a Cinvestav located on Guadalajara.
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ahh ok hehe
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Does you gf speaks english?
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I even have some of the (admission or entrance?) exams. Let me see..
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Yeah, which has really slowed me down. She has no patience. Everytime I ask her something she says 'that's stupid, why would you ask that?'
I will be looking into that school here, I kinda like Guadalajara, and after living in LA for 12 years I don't really want to move to DF
more expensive to, right?
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cool!
entrance exam is the term, what is it in spanish?
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Examen de admisión. That is the reason I get confused.
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right, I tried to say pagar atencion once, I got laughed at, but that's what it is in english "pay attention" not "put attention"
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again sorry for not having accent marks...
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Don't worry 70% of mexicans don't know how to use the accent marks.
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But is good that you learn how to use them.
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My roomate spoke spanish at home all his life and was born in DF, but I correct him on things sometimes because I'm learning spanish formally. He never did that.
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You mean your roomate at LA?
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No, here in GDL
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Ahh.
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I think we have the same time zone, right?
I know it's not that late, but I think I should try to sleep. I have to do 2 weeks worth of homework tomorrow =(
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Yeah, it's better to go to sleep. I'm still looking for the entrance exam.
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Thanks for the info on Cinvestav, I'll look into it. And looking for the exam. If you find it I'd be curious to hear what it has.
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Ok, Have a good night, I'm goint to be here tomorrow in case you need some help.
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I may have to take you up on that, thanks!
goodnight No-Data.
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to what?
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what does it means to take something up?
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"to take someone up on an offer"
I said I'd have to take you up on your offer, meaning I may ask you for help with spanish.
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or just, 'I might take you up on that' for short
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Ahh thanks!
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Well is difficult to learn that in a book or with google traslator. thank you so much. And have a good night again
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yeah expressions are tricky...
goodnight :D