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Help me with combinations

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jim441
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Help me with combinations [#permalink] New post   19 Apr 2023, 04:45
Ques: we have to make a reading list of 4 from 5 novels and 3 articles such that we have 2 novels and 2 articles.

How are we going to solve in both the cases when order matters and order doesn't matter?

I have a confusion coz of the below mentioned thing:
so we have to make a four digit number such that every digit is distnict.

Answer to this question will be 9*9*8*7

In the above question we dont have to take order into consideration, coz whenever we multiply we already take order into consideration.
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MartyTargetTestPrep
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Re: Help me with combinations [#permalink] New post   19 Apr 2023, 12:59
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jim441 wrote:
Ques: we have to make a reading list of 4 from 5 novels and 3 articles such that we have 2 novels and 2 articles.

How are we going to solve in both the cases when order matters and order doesn't matter?

Order doesn't ever matter in that question.

You just find how many sets of two novels and sets of two articles you can choose and multiply the number of sets of novels by the numbers of sets of books.
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jim441
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Re: Help me with combinations [#permalink] New post   19 Apr 2023, 13:03
MartyTargetTestPrep wrote:
jim441 wrote:
Ques: we have to make a reading list of 4 from 5 novels and 3 articles such that we have 2 novels and 2 articles.

How are we going to solve in both the cases when order matters and order doesn't matter?

Order doesn't ever matter in that question.

You just find how many sets of two novels and sets of two articles you can choose and multiply the number of sets of novels by the numbers of sets of books.


All I want to know is if I multiply 5C2 and 3C2, Am I considering all the ordered pairs??
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MartyTargetTestPrep
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Re: Help me with combinations [#permalink] New post   19 Apr 2023, 13:45
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jim441 wrote:
MartyTargetTestPrep wrote:
jim441 wrote:
Ques: we have to make a reading list of 4 from 5 novels and 3 articles such that we have 2 novels and 2 articles.

How are we going to solve in both the cases when order matters and order doesn't matter?

Order doesn't ever matter in that question.

You just find how many sets of two novels and sets of two articles you can choose and multiply the number of sets of novels by the numbers of sets of books.


All I want to know is if I multiply 5C2 and 3C2, Am I considering all the ordered pairs??

You are considering all the pairs, but they are not ordered. They are unordered combinations.
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EMPOWERgmatRichC
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Re: Help me with combinations [#permalink] New post   19 Apr 2023, 16:30
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Hi jim441,

The 'style' of the question that you are asking about heavily implies that you are dealing with a COMBINATION question (if you are forming groups of books/articles to read, then the order in which you read them does not matter). In this situation, the proper calculation would be:

(5c2)(3c2)

IF you were dealing with a situation in which the order of the items DID matter, then the prompt would almost certainly include information to define those limitations. For example, it might state, "how many arrangements of books/articles can be made if the two novels are read first and last?"

GMAT assassins aren't born, they're made,
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Contact Rich at: Rich.C@empowergmat.com
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GMATWhizTeam
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Re: Help me with combinations [#permalink] New post   20 Apr 2023, 00:02
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Here's a playlist that you may find helpful in order to ace Permutation and Combination Qs:

https://www.youtube.com/playlist?list=P ... nASu4rT5Dh
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jim441
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Re: Help me with combinations [#permalink] New post   21 Apr 2023, 09:12
MartyTargetTestPrep wrote:
jim441 wrote:
MartyTargetTestPrep wrote:
Order doesn't ever matter in that question.

You just find how many sets of two novels and sets of two articles you can choose and multiply the number of sets of novels by the numbers of sets of books.


All I want to know is if I multiply 5C2 and 3C2, Am I considering all the ordered pairs??

You are considering all the pairs, but they are not ordered. They are unordered combinations.


I still dont understand the concept.
Check this question out : https://gmatclub.com/forum/in-how-many- ... 85707.html

In the above question, by multiplying we have consiered all the ordered pairs.
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MartyTargetTestPrep
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Help me with combinations [#permalink] New post   21 Apr 2023, 14:39
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jim441 wrote:
I still dont understand the concept.
Check this question out : https://gmatclub.com/forum/in-how-many- ... 85707.html

In the above question, by multiplying we have consiered all the ordered pairs.

Actually, the pairs are not ordered in that question either.

This post could help you to understand why.

GMAT permutations and combinations: Which One to Use?
GMAT Club Bot
gmatclubot
Help me with combinations [#permalink]
21 Apr 2023, 14:39
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