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# A number is to be selected at random from the set above

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Manager
Joined: 16 Feb 2012
Posts: 237
Concentration: Finance, Economics
Followers: 7

Kudos [?]: 202 [0], given: 121

A number is to be selected at random from the set above [#permalink]

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01 May 2012, 02:30
00:00

Difficulty:

35% (medium)

Question Stats:

70% (01:41) correct 30% (00:48) wrong based on 82 sessions

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

A number is to be 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?

A. 1/12
B. 1/6
C. 1/4
D. 1/3
E. 1/2
[Reveal] Spoiler: OA

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Last edited by Bunuel on 01 May 2012, 02:41, edited 1 time in total.
Edited the question and added the OA
Math Expert
Joined: 02 Sep 2009
Posts: 33000
Followers: 5751

Kudos [?]: 70481 [0], given: 9847

Re: A number is to be selected at random from the set above [#permalink]

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01 May 2012, 02:44
Expert's post
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Stiv wrote:
{-10, -6, -5, -4, -2.5, -1, 0, 2.5, 4, 6, 7, 10}

A number is to be 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?

A. 1/12
B. 1/6
C. 1/4
D. 1/3
E. 1/2

Roots of the equation (x-5)(x+10)(2x-5)=0 are x=5, x=-10 and x=5/2=2.5. So, two solutions present in our set of 12 distinct numbers, therefore P=2/12=1/6.

_________________
Manager
Joined: 16 Feb 2012
Posts: 237
Concentration: Finance, Economics
Followers: 7

Kudos [?]: 202 [0], given: 121

Re: A number is to be selected at random from the set above [#permalink]

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02 May 2012, 00:39
Aaaaaa OMG, I actually didn't notice that there isn't number 5(positive) in this bunch of numbers. I assumed it, and I got it wrong!

My advice to everyone: Don't assume anything!!!
_________________

Kudos if you like the post!

Failing to plan is planning to fail.

Re: A number is to be selected at random from the set above   [#permalink] 02 May 2012, 00:39
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