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# A number is selected at random from the set above. what is the probabi

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Manager
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Kudos [?]: 156 [0], given: 15

A number is selected at random from the set above. what is the probabi [#permalink]

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25 Oct 2010, 07:43
00:00

Difficulty:

25% (medium)

Question Stats:

58% (01:46) correct 42% (00:16) wrong based on 24 sessions

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{-10,-6,-5,-4,-2.5,-1,0,2.5,4,6,7,10}

A number is selected at random from the set above. what is the probability that the number selected will be a solution of the equation (x-5)(x+10)(2x-5)=0?

1/12
1/6
1/4
1/3
1/2
[Reveal] Spoiler: OA
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Posts: 38908
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Kudos [?]: 106256 [0], given: 11618

Re: A number is selected at random from the set above. what is the probabi [#permalink]

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25 Oct 2010, 07:50
vanidhar wrote:
{-10, -6, -5, -4, -2.5, -1, 0, 2.5, 4, 6, 7, 10}

A number is selectedat random from the set above. what is the probablitiy that the number selected will be a solution of the equation (x-5)(x+10)(2x-5)=0?
1/12
1/6
1/4
1/3
1/2

Solutions of the equation $$(x-5)(x+10)(2x-5)=0$$ are: $$x=5$$, $$x=-10$$ and $$x=2.5$$.

There are total of 12 numbers in the set {-10, -6, -5, -4, -2.5, -1, 0, 2.5, 4, 6, 7, 10} and it contains 2 roots: -10 and 2,5, so the probablitiy that the number selected will be a solution of the given equation is $$P=\frac{2}{12}=\frac{1}{6}$$.

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Manager
Status: GMAT Preperation
Joined: 04 Feb 2010
Posts: 101
Concentration: Social Entrepreneurship, Social Entrepreneurship
GPA: 3
WE: Consulting (Insurance)
Followers: 2

Kudos [?]: 156 [0], given: 15

Re: A number is selected at random from the set above. what is the probabi [#permalink]

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26 Oct 2010, 00:39
it contains 2 roots: -10 and 2.5 ??
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Kudos [?]: 1020 [0], given: 25

Re: A number is selected at random from the set above. what is the probabi [#permalink]

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26 Oct 2010, 00:45
vanidhar wrote:
it contains 2 roots: -10 and 2.5 ??

Roots = Solution to the equation

We know the only solutions are -10,2.5,5
And of these, two are present in the set at hand
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Re: A number is selected at random from the set above. what is the probabi   [#permalink] 26 Oct 2010, 00:45
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