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# Probability - when does order matter?

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Manager
Joined: 13 Dec 2013
Posts: 161
Location: United States (NY)
GMAT 1: 710 Q46 V41
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WE: Consulting (Consulting)
Probability - when does order matter?  [#permalink]

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07 Apr 2017, 16:50
Hi All,

I've been trying to get the concept of order clear in my mind, i.e. when does the order need to be accounted for and when does it not? Please comment on whether you agree with following rule and add additional information if you have it. Having looked through the probability guides I could not find a clear answer to this question.

Order matters only when you use consecutive multiplication - in these cases you must find all possible orders in which the desired event can occur.
Manager
Joined: 26 Dec 2011
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Location: United States (NY)
Concentration: Finance, Entrepreneurship
GPA: 3.4
WE: Investment Banking (Investment Banking)
Re: Probability - when does order matter?  [#permalink]

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09 Apr 2017, 14:02
Whether or not order matters will be determined on a case-by-case basis. If you are selecting 3 people for a team (i.e. you're either on the team or not), order doesn't matter. If you are selecting 3 people for 3 different positions on the team (e.g. president, VP, secretary), order does matter.
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Manager
Joined: 13 Dec 2013
Posts: 161
Location: United States (NY)
GMAT 1: 710 Q46 V41
GMAT 2: 720 Q48 V40
GPA: 4
WE: Consulting (Consulting)
Re: Probability - when does order matter?  [#permalink]

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09 Apr 2017, 20:47
okay wrote:
Whether or not order matters will be determined on a case-by-case basis. If you are selecting 3 people for a team (i.e. you're either on the team or not), order doesn't matter. If you are selecting 3 people for 3 different positions on the team (e.g. president, VP, secretary), order does matter.

Thanks for your reply but I'm talking about order with regard to probability and not just general order.
Manager
Joined: 19 Feb 2010
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Re: Probability - when does order matter?  [#permalink]

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14 Apr 2017, 16:56
Cez005 wrote:
okay wrote:
Whether or not order matters will be determined on a case-by-case basis. If you are selecting 3 people for a team (i.e. you're either on the team or not), order doesn't matter. If you are selecting 3 people for 3 different positions on the team (e.g. president, VP, secretary), order does matter.

Thanks for your reply but I'm talking about order with regard to probability and not just general order.

Hi Cez,

Your understanding is apt. What 'Okay' gave is an example for the rule you wrote.

A general tip that I would like to give you is that whenever you are caught in this dilemma, try to ask yourself, whether it is the case of "selection" or "arrangement". Generally, order does not matter in "selection" and it does so in "selections".

Examples:
1. A team of five is selected from a group of four boys and seven girls. What is the probability that no boy is selected?
A case of selection and hence, the order shall not matter (in numerator as well as denominator).

2. Letters of the word COMPUTER are shuffled. What is the probability that C comes before both O and U?
A case of arrangement and hence, the order shall matter (in numerator as well as denominator).

Hope that helps!

All the best!
Maxximus
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Re: Probability - when does order matter? &nbs [#permalink] 14 Apr 2017, 16:56
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