probablity for an eq : GMAT Problem Solving (PS)
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# probablity for an eq

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Manager
Status: GMAT Preperation
Joined: 04 Feb 2010
Posts: 103
Concentration: Social Entrepreneurship, Social Entrepreneurship
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Kudos [?]: 147 [0], given: 15

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25 Oct 2010, 06:43
00:00

Difficulty:

25% (medium)

Question Stats:

61% (01:46) correct 39% (00:18) wrong based on 23 sessions

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{-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
[Reveal] Spoiler: OA
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Posts: 37024
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Kudos [?]: 96043 [0], given: 10706

Re: probablity for an eq [#permalink]

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25 Oct 2010, 06:50
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 $$P=\frac{2}{12}=\frac{1}{6}$$.

_________________
Manager
Status: GMAT Preperation
Joined: 04 Feb 2010
Posts: 103
Concentration: Social Entrepreneurship, Social Entrepreneurship
GPA: 3
WE: Consulting (Insurance)
Followers: 2

Kudos [?]: 147 [0], given: 15

Re: probablity for an eq [#permalink]

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25 Oct 2010, 23:39
it contains 2 roots: -10 and 2.5 ??
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Kudos [?]: 971 [0], given: 25

Re: probablity for an eq [#permalink]

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25 Oct 2010, 23:45
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
_________________
Re: probablity for an eq   [#permalink] 25 Oct 2010, 23:45
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