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# M10-14

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Intern
Joined: 14 Aug 2017
Posts: 14
Re: M10-14  [#permalink]

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30 Aug 2018, 19:42
Hi Bunuel,

Does this 'Not necessarily different' terminology given in the question implies that the number is not repeated?
Because when I first attempted this question i got 1/2 i.e . (1/4)*(3/3) + (3/4)*(1/3) = (1/2)

But now when I saw your solution, I came to know that the numbers should not be reduced and should be kept same.
I just wanted to get it confirmed with you that everytime in future if I see this term 'Not necessarily different' should I consider that the number is not repeated?
Math Expert
Joined: 02 Sep 2009
Posts: 51229
Re: M10-14  [#permalink]

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30 Aug 2018, 20:00
1
varmashreekanth wrote:
Hi Bunuel,

Does this 'Not necessarily different' terminology given in the question implies that the number is not repeated?
Because when I first attempted this question i got 1/2 i.e . (1/4)*(3/3) + (3/4)*(1/3) = (1/2)

But now when I saw your solution, I came to know that the numbers should not be reduced and should be kept same.
I just wanted to get it confirmed with you that everytime in future if I see this term 'Not necessarily different' should I consider that the number is not repeated?

If a number is selected from set S at random and then another number, not necessarily different, is selected from set S at random, ...

The highlighted part in the question means that from S={2,3,5,7} we can choose any number more than once. So, we can choose the following two numbers:
(2,2)
(2,3)
(3,2)
(2,5)
(5,2)
(2,7)
(7,2)

(3,3)
(3,5)
(5,3)
(3,7)
(7,3)
(5,5)
(5,7)
(7,5)
(7,7)
_________________
Intern
Joined: 14 Aug 2017
Posts: 14
Re: M10-14  [#permalink]

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30 Aug 2018, 21:07
Thanks a lot Bunuel. Now I understood the scenario.
Intern
Joined: 26 Aug 2017
Posts: 11
Re: M10-14  [#permalink]

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23 Sep 2018, 13:28
susheelh wrote:
Hello Bunuel

I think this is a high-quality question and I agree with the solution. I have the same conceptual gap as Demba below. Can you please help?

Usually, for questions like these, I find the total possibilities first and then the favourable outcomes. To do this, its necessary to know if the order of outcome matters.

Clearly, in this question order matters. (2,3) is different from (3,2). How do we understand after reading the question that order matters? Is it because the question says 'not necessarily different' which implies repetition is allowed?

I was comparing this solution with this one - https://gmatclub.com/forum/m20-184246.html#p1859217. In this solution that I pasted, Order does not matter. So, we wanted to know how to decide after reading a question if order matters or no.

I hope I was able to communicate what I intend to say.

Thanking you in advance!

Demba wrote:
I struggle to know when order matters. Why is the answer not simply 1/4*3/4?

Why is picking 2 then 3 or 5 or 7 different from picking picking 3 or 5 or 7 then 2?

Bumping
Re: M10-14 &nbs [#permalink] 23 Sep 2018, 13:28

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# M10-14

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Moderators: chetan2u, Bunuel

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