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# One number, n, is selected at random from a set of 10 integers. What

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Math Expert
Joined: 02 Sep 2009
Posts: 52906
One number, n, is selected at random from a set of 10 integers. What  [#permalink]

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19 May 2016, 02:29
00:00

Difficulty:

55% (hard)

Question Stats:

60% (01:54) correct 40% (01:38) wrong based on 173 sessions

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One number, n, is selected at random from a set of 10 integers. What is the probability that 1/2*n + 13 = 0 ?

(1) The largest integer in the set is 13.
(2) The arithmetic mean of the set is zero.

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Joined: 02 Aug 2009
Posts: 7334
Re: One number, n, is selected at random from a set of 10 integers. What  [#permalink]

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19 May 2016, 02:54
1
1
Bunuel wrote:
One number, n, is selected at random from a set of 10 integers. What is the probability that 1/2*n + 13 = 0 ?

(1) The largest integer in the set is 13.
(2) The arithmetic mean of the set is zero.

The Q can be rephrased-
$$\frac{1}{2}* n + 13 =0............n=-13*2=-26$$...............
so there are 10 integers and we have to find that what is the probability of the integer,n, being picked to be -26....
HAD the Q said been - a set of 10 DIFFERENT integers, our answer would be 1/10, but we do not know how many of 10 integers are -26...

(1) The largest integer in the set is 13.
we do not know anything about other 9 numbers
Insuff

(2) The arithmetic mean of the set is zero.

It just tells us that mean is 0, can be any variation..

Combined-
lot of variation can be made where the largest number is 13 and the mean is 0..
example 13,13,0,0,0,0,0,0,0,-26... prob = 1/10
13, 10,10,10,3,3,3,0,-26,-26..... Now prob = 2/10
Insuff
E
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1) Absolute modulus : http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372
2)Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html
3) effects of arithmetic operations : https://gmatclub.com/forum/effects-of-arithmetic-operations-on-fractions-269413.html
4) Base while finding % increase and % decrease : https://gmatclub.com/forum/percentage-increase-decrease-what-should-be-the-denominator-287528.html

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Re: One number, n, is selected at random from a set of 10 integers. What  [#permalink]

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04 May 2017, 15:01
I picked E...a tricky one..
i initially thought we have consecutive integers, but then read second statement, and immediately knew that we can't find the answer...
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Joined: 17 Apr 2016
Posts: 87
Re: One number, n, is selected at random from a set of 10 integers. What  [#permalink]

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15 May 2017, 19:12
chetan2u wrote:
Bunuel wrote:
One number, n, is selected at random from a set of 10 integers. What is the probability that 1/2*n + 13 = 0 ?

(1) The largest integer in the set is 13.
(2) The arithmetic mean of the set is zero.

The Q can be rephrased-
$$\frac{1}{2}* n + 13 =0............n=-13*2=-26$$...............
so there are 10 integers and we have to find that what is the probability of the integer,n, being picked to be -26....
HAD the Q said been - a set of 10 DIFFERENT integers, our answer would be 1/10, but we do not know how many of 10 integers are -26...

(1) The largest integer in the set is 13.
we do not know anything about other 9 numbers
Insuff

(2) The arithmetic mean of the set is zero.

It just tells us that mean is 0, can be any variation..

Combined-
lot of variation can be made where the largest number is 13 and the mean is 0..
example 13,13,0,0,0,0,0,0,0,-26... prob = 1/10
13, 10,10,10,3,3,3,0,-26,-26..... Now prob = 2/10
Insuff
E

chetan2u,
For Statement A, I agree that the probability of choosing -26 would have been 1/10, but this would again be the case provided that it is given that -26 is a part of the set.
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Joined: 02 Aug 2018
Posts: 70
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GMAT 1: 590 Q45 V26
GPA: 3.5
Re: One number, n, is selected at random from a set of 10 integers. What  [#permalink]

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16 Oct 2018, 05:11
chetan2u wrote:
Bunuel wrote:
One number, n, is selected at random from a set of 10 integers. What is the probability that 1/2*n + 13 = 0 ?

(1) The largest integer in the set is 13.
(2) The arithmetic mean of the set is zero.

The Q can be rephrased-
$$\frac{1}{2}* n + 13 =0............n=-13*2=-26$$...............
so there are 10 integers and we have to find that what is the probability of the integer,n, being picked to be -26....
HAD the Q said been - a set of 10 DIFFERENT integers, our answer would be 1/10, but we do not know how many of 10 integers are -26...

(1) The largest integer in the set is 13.
we do not know anything about other 9 numbers
Insuff

(2) The arithmetic mean of the set is zero.

It just tells us that mean is 0, can be any variation..

Combined-
lot of variation can be made where the largest number is 13 and the mean is 0..
example 13,13,0,0,0,0,0,0,0,-26... prob = 1/10
13, 10,10,10,3,3,3,0,-26,-26..... Now prob = 2/10
Insuff
E

chetan2u,
For Statement A, I agree that the probability of choosing -26 would have been 1/10, but this would again be the case provided that it is given that -26 is a part of the set.

I have the same question, any reasons that we can say probability would be 1/10 if in case n were categorically mentioned as dufferent integers ?

Re: One number, n, is selected at random from a set of 10 integers. What   [#permalink] 16 Oct 2018, 05:11
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