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probability that ½ n + 13 = 0

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by sanju09 » Mon Jul 26, 2010 2:37 am
One number, n, is selected at random from a set of 10 integers. What is the probability that ½ n + 13 = 0?

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

[spoiler]Source: majortests.com[/spoiler]
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Source: — Data Sufficiency |
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by kvcpk » Mon Jul 26, 2010 5:38 am
sanju09 wrote:One number, n, is selected at random from a set of 10 integers. What is the probability that ½ n + 13 = 0?

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

[spoiler]Source: majortests.com[/spoiler]
n/2 + 13 = 0
-> n= -26

Question is askign what is the probability that n will be -26.

The largest integer in the set is 13.

-26 may / may not be present in the set of 10 integers even when largest integer is 13.
hence INSUFF

The arithmetic mean of the set is zero.
Arithmetic means is 0 means that the sum of the numbers is 0.
This also doesnt tell anything about -26 in the list.

Combining:
set can be
-1,-2,-3,-4,-3,-6,-7,7,6,13
In this case probability that n is -26 is 0
set can be:
-26,-13,13,13,13,2,-2,-1,1
in this case probability is 1/10
2 different answers.

Hence INSUFF

pick E
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