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# Pick 5 numbers from 1 to 20 (integer), what is the

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Pick 5 numbers from 1 to 20 (integer), what is the [#permalink]

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13 Sep 2004, 13:20
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Pick 5 numbers from 1 to 20 (integer), what is the probability that the 5 numbers include 10 and 20?
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Re: PS - Probability [#permalink]

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13 Sep 2004, 13:36
mba4me wrote:
Pick 5 numbers from 1 to 20 (integer), what is the probability that the 5 numbers include 10 and 20?

i would say:

20c2/20c5

is there a good chance of anything like this on the gmat?
Joined: 31 Dec 1969
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21 Oct 2004, 15:06
sorry guys.....

please, i dont got it..... can you explain how do you obtain 18C3 as the number of probable events? .... thanks

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21 Oct 2004, 20:55
Hello Guest,

Please sign up and give yourself an identity on this club.

--Bhai
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22 Oct 2004, 04:30
nzgmat wrote:
I also agree

10C3/20C5

Hi, can you please explain how you got 18C3/20C5?
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Paul

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22 Oct 2004, 13:41
opss.....

Guest identified: me! (sorry that i forgot to login)

Hi, same question... can you explain how you got 18C3/20C5?

thanks guys
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22 Oct 2004, 14:07
I also don't see whether repitition is allowed or not?

*** no repetition ***
total ways = 20C5
no 10s or 20s = 18C5

10 and/or a 20
(1-18C5)/20C5

*** with repitition ***

No 10s and no 20s
5 failures
5C5*(18/20)^5

at least one 10 or 20
1-(18/20)^5
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22 Oct 2004, 15:56
guys let us make things easier.

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peace out ........

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24 Oct 2004, 00:07
Oh well, here is the explanation then
favorable outcomes when 10 and 20 are included: 18C3 --> Because you have only 3 more numbers (out of 5) to pick from the 18 remaining numbers since 10 and 20 are already out.
Total favorable outcomes: 20C5 --> # of ways to pick 5 items out of 20 where order does not matter
Probability of picking 5 numbers which include #10 and #20: 18C3/20C5

Guys, try to explain the answer to fellow members who request such help. Simply saying the answer or "I agree with the answer" does not add to the discussion. Thanks.
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Paul

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24 Oct 2004, 16:42
Got it !!

Thanks Paul and mba4me !

good question
24 Oct 2004, 16:42
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# Pick 5 numbers from 1 to 20 (integer), what is the

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