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# In how many ways can you select three integers x1, x2 &

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Senior Manager
Joined: 22 Aug 2003
Posts: 257
Location: Bangalore

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In how many ways can you select three integers x1, x2 & [#permalink]

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08 Sep 2003, 04:11
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

In how many ways can you select three integers x1, x2 & x3 from 1 to 12 such that x1<x2<x3. (Hint: Two ways to solve this. One lengthy...uhh and one very shorte... ahh)
-Vicks

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CEO
Joined: 15 Aug 2003
Posts: 3454

Kudos [?]: 886 [0], given: 781

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08 Sep 2003, 09:06
javropu wrote:
id say 220

can u explain javs?

Kudos [?]: 886 [0], given: 781

Manager
Joined: 14 Aug 2003
Posts: 88
Location: barcelona

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08 Sep 2003, 09:52
id do the following:
12*11*10/(3!)=220

Kudos [?]: 886 [0], given: 0

CEO
Joined: 15 Aug 2003
Posts: 3454

Kudos [?]: 886 [0], given: 781

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08 Sep 2003, 10:45
javropu wrote:
id do the following:
12*11*10/(3!)=220

But ...did you use 12C3 ??
Isnt 12C3 the total # of ways to draw 3 from 1-12 numbers without any restrictions?

Praetorian

Kudos [?]: 886 [0], given: 781

Senior Manager
Joined: 22 Aug 2003
Posts: 257
Location: Bangalore

Kudos [?]: 13 [0], given: 0

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08 Sep 2003, 21:38
right javs...
12C3 is the number of ways to select three numbers, and there is only one
way to arrange these numbers such that x1<x2<x3
i hope u got it praet...
-Vikcs

Kudos [?]: 13 [0], given: 0

CEO
Joined: 15 Aug 2003
Posts: 3454

Kudos [?]: 886 [0], given: 781

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11 Sep 2003, 04:04
Vicky wrote:
right javs...
12C3 is the number of ways to select three numbers, and there is only one
way to arrange these numbers such that x1<x2<x3
i hope u got it praet...
-Vikcs

Clever way of phrasing the problem..same as the # of ways to pick 3 #'s from 1-12..

Thanks!

Kudos [?]: 886 [0], given: 781

Intern
Joined: 21 Jul 2003
Posts: 8

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11 Sep 2003, 13:19
if order does matter than why are we using a combination formula?

shouldn't we use the permutation formula?

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CEO
Joined: 15 Aug 2003
Posts: 3454

Kudos [?]: 886 [0], given: 781

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11 Sep 2003, 18:27
lakrana wrote:
if order does matter than why are we using a combination formula?

shouldn't we use the permutation formula?

If order matters ,we use permutations..
Permutations say the every position is unique..so 123 is different from 321...

But in our case...we dont need the positions to be unique..

hth
praetorian

Kudos [?]: 886 [0], given: 781

Re: still confused   [#permalink] 11 Sep 2003, 18:27
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