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Hello,
I have a question:
For Statement 1:
if we take consecutive even numbers {2,4,6}:
When lowest number is removed, set becomes {4,6} - the average 5
When the highest number is removed, set becomes {2,4} - the average is 3.
Why above presented can not prove statement 1 as insufficient?
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futurephilantropist
Hello,
I have a question:
For Statement 1:
if we take consecutive even numbers {2,4,6}:
When lowest number is removed, set becomes {4,6} - the average 5
When the highest number is removed, set becomes {2,4} - the average is 3.
Why above presented can not prove statement 1 as insufficient?

Hi futurephilantropist,

TESTing VALUES is a great way to approach this question, but you have to choose values that 'fit' the given information. The information in Fact 1 tells us that the difference in the two averages is 1. In your example, the difference is 2 - so your example is not applicable.

GMAT assassins aren't born, they're made,
Rich
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HI GMAT Assassin/Co-Founder,

Thank you so much for the answer. It does make sense now.
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Bunuel
A list contains n distinct integers. Are all n integers consecutive?

Notice that we are told that the list contains distinct integers.

Say the numbers in the list in ascending order are: \(x_1\), \(x_2\), ..., \(x_n\).

(1) The average (arithmetic mean) of the list with the lowest number removed is 1 more than the average (arithmetic mean) of the list with the highest number removed.

\(\frac{x_2+x_3+...+x_n}{n-1}=\frac{x_1+x_2+...+x_{n-1}}{n-1}+1\);

\(x_n=x_1+n-1\).

The above implies that:
\(x_2=x_1+1\);
\(x_3=x_1+2\);
...

Therefore the integers in the list are consecutive. Sufficient.

(2) The positive difference between any two numbers in the list is always less than n. This holds true for any list of consecutive integers: even the difference between the largest and smallest elements must be less than the number of elements (n). For example, {1, 2, 3} --> 3-1=2<3. Since we are told that the list contains distinct integers, then no other set than the set of consecutive integers can satisfy that. Sufficient.

Answer: D.

Hope it's c;ear.

Hello Bunuel,
Could you please explain how did you go from this \(\frac{x_2+x_3+...+x_n}{n-1}=\frac{x_1+x_2+...+x_{n-1}}{n-1}+1\); to this \(x_n=x_1+n-1\). ? I can't figure out the process behind the reasoning.
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Bunuel
A list contains n distinct integers. Are all n integers consecutive?

Notice that we are told that the list contains distinct integers.

Say the numbers in the list in ascending order are: \(x_1\), \(x_2\), ..., \(x_n\).

(1) The average (arithmetic mean) of the list with the lowest number removed is 1 more than the average (arithmetic mean) of the list with the highest number removed.

\(\frac{x_2+x_3+...+x_n}{n-1}=\frac{x_1+x_2+...+x_{n-1}}{n-1}+1\);

\(x_n=x_1+n-1\).

The above implies that:
\(x_2=x_1+1\);
\(x_3=x_1+2\);
...

Therefore the integers in the list are consecutive. Sufficient.

(2) The positive difference between any two numbers in the list is always less than n. This holds true for any list of consecutive integers: even the difference between the largest and smallest elements must be less than the number of elements (n). For example, {1, 2, 3} --> 3-1=2<3. Since we are told that the list contains distinct integers, then no other set than the set of consecutive integers can satisfy that. Sufficient.

Answer: D.

Hope it's c;ear.

Hello Bunuel,
Could you please explain how did you go from this \(\frac{x_2+x_3+...+x_n}{n-1}=\frac{x_1+x_2+...+x_{n-1}}{n-1}+1\); to this \(x_n=x_1+n-1\). ? I can't figure out the process behind the reasoning.


Multiply \(\frac{x_2+x_3+...+x_n}{n-1}=\frac{x_1+x_2+...+x_{n-1}}{n-1}+1\) by n - 1:

\((x_2+x_3+...+x_n)=(x_1+x_2+...+x_{n-1})+(n-1)\);

Notice that you can cancel \(x_2+...+x_{n-1}\) from both sides and you get: \(x_n=x_1+(n-1)\).

Hope it's clear.
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A list contains n distinct integers. Are all n integers consecutive?

Stat1: The average (arithmetic mean) of the list with the lowest number removed is 1 more than the average (arithmetic mean) of the list with the highest number removed.

(x2+x3)/2= (x1+x2)/2 + 1, or, x3= x1 + 2 , so sufficient as x1, x2 and x3 are consecutive.

Stat2: The positive difference between any two numbers in the list is always less than n
It means, even there are 2 numbers, then their difference should be less than 2, which is 1 or 2. but, there are distinct integers. So sufficient.

Ans. D. :)
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Bunuel
A list contains n distinct integers. Are all n integers consecutive?

Notice that we are told that the list contains distinct integers.

Say the numbers in the list in ascending order are: \(x_1\), \(x_2\), ..., \(x_n\).

(1) The average (arithmetic mean) of the list with the lowest number removed is 1 more than the average (arithmetic mean) of the list with the highest number removed.

\(\frac{x_2+x_3+...+x_n}{n-1}=\frac{x_1+x_2+...+x_{n-1}}{n-1}+1\);

\(x_n=x_1+n-1\).

The above implies that:
\(x_2=x_1+1\);
\(x_3=x_1+2\);
...

Therefore the integers in the list are consecutive. Sufficient.

(2) The positive difference between any two numbers in the list is always less than n. This holds true for any list of consecutive integers: even the difference between the largest and smallest elements must be less than the number of elements (n). For example, {1, 2, 3} --> 3-1=2<3. Since we are told that the list contains distinct integers, then no other set than the set of consecutive integers can satisfy that. Sufficient.

Answer: D.

Hope it's c;ear.


Statement 1 is not sufficient

take the set
{ -1, 1, 2, 3 }

if we take the lowest out the mean is 2
if we take the highest out the mean is 1
but it is not consecutive .
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Bunuel
A list contains n distinct integers. Are all n integers consecutive?

Notice that we are told that the list contains distinct integers.

Say the numbers in the list in ascending order are: \(x_1\), \(x_2\), ..., \(x_n\).

(1) The average (arithmetic mean) of the list with the lowest number removed is 1 more than the average (arithmetic mean) of the list with the highest number removed.

\(\frac{x_2+x_3+...+x_n}{n-1}=\frac{x_1+x_2+...+x_{n-1}}{n-1}+1\);

\(x_n=x_1+n-1\).

The above implies that:
\(x_2=x_1+1\);
\(x_3=x_1+2\);
...

Therefore the integers in the list are consecutive. Sufficient.

(2) The positive difference between any two numbers in the list is always less than n. This holds true for any list of consecutive integers: even the difference between the largest and smallest elements must be less than the number of elements (n). For example, {1, 2, 3} --> 3-1=2<3. Since we are told that the list contains distinct integers, then no other set than the set of consecutive integers can satisfy that. Sufficient.

Answer: D.

Hope it's c;ear.
Statement 1 is not sufficient

take the set
{ -1, 1, 2, 3 }

if we take the lowest out the mean is 2
if we take the highest out the mean is 1
but it is not consecutive .

{-1, 1, 2, 3 } does not satisfy (1)

\(\frac{1+2+3}{4-1} \neq \frac{-1+1+2}{4-1}+1\).
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Bunuel
A list contains n distinct integers. Are all n integers consecutive?

Notice that we are told that the list contains distinct integers.

Say the numbers in the list in ascending order are: \(x_1\), \(x_2\), ..., \(x_n\).

(1) The average (arithmetic mean) of the list with the lowest number removed is 1 more than the average (arithmetic mean) of the list with the highest number removed.

\(\frac{x_2+x_3+...+x_n}{n-1}=\frac{x_1+x_2+...+x_{n-1}}{n-1}+1\);

\(x_n=x_1+n-1\).

The above implies that:
\(x_2=x_1+1\);
\(x_3=x_1+2\);
...

Therefore the integers in the list are consecutive. Sufficient.

(2) The positive difference between any two numbers in the list is always less than n. This holds true for any list of consecutive integers: even the difference between the largest and smallest elements must be less than the number of elements (n). For example, {1, 2, 3} --> 3-1=2<3. Since we are told that the list contains distinct integers, then no other set than the set of consecutive integers can satisfy that. Sufficient.

Answer: D.

Hope it's c;ear.

Hi Bunuel , No matter what case I take I feel statement will always be applicable . Can you please share an example of any list when this is not the case. Thank you
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