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Pick 5 numbers at random from integers 1 to 20. What is the

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Pick 5 numbers at random from integers 1 to 20. What is the [#permalink] New post 14 Sep 2004, 08:03
Pick 5 numbers at random from integers 1 to 20. What is the probability that the 5 numbers picked includes the numbers 10 & 20?
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 [#permalink] New post 14 Sep 2004, 08:09
Nevermind! I found the same question posted earlier. Heres the link but I'm not sure about the answer. Lovely - Can you please explain a bit more on how you arrived at the solution?

http://www.gmatclub.com/phpbb/viewtopic.php?t=9774
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 [#permalink] New post 14 Sep 2004, 09:45
lovely wrote:
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?


Is this the OA?
I did as below:

Pb of getting 10 and 20
= 1 - Pb of not getting 10 and 20
= 1 - 18C5/20C5
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 [#permalink] New post 15 Sep 2004, 08:51
48/273

Whats the OA?
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 [#permalink] New post 15 Sep 2004, 09:11
OA - 17/38. I think hardworkers method fetches me the OA. Thanks guys!
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 [#permalink] New post 15 Sep 2004, 10:50
The snwer shd be 19C3/21C5. We shd not forget tht between 1 and 20, there are 21 numbers.
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 [#permalink] New post 18 Sep 2004, 16:07
Sdanquah : there are 20 numbers between 1 and 20, remember the formula (last-first)+1= 20-1+1= 20

Could someone please explain the OA ?

I used the same way as hardworker with 1- prob not to be selected =
1- 18C5/20C5 and obtained 21/38
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 [#permalink] New post 18 Sep 2004, 21:50
twixt wrote:
Sdanquah : there are 20 numbers between 1 and 20, remember the formula (last-first)+1= 20-1+1= 20

Could someone please explain the OA ?

I used the same way as hardworker with 1- prob not to be selected =
1- 18C5/20C5 and obtained 21/38


1- 18C5/20C5
= 1 - 15x14/20x19
= 1 - 21/38
= 17/38

I think you forgot to subtract from 1 :wink:
  [#permalink] 18 Sep 2004, 21:50
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