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Set X consists of seven consecutive integers, and Set Y [#permalink]
03 Mar 2012, 05:41

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Difficulty:

55% (medium)

Question Stats:

42% (02:10) correct
58% (01:28) wrong based on 191 sessions

Set X consists of seven consecutive integers, and Set Y consists of nine consecutive integers. Is the median of the numbers in set X equal to the median of the numbers in set Y?

(1) The sum of the numbers in set X is equal to the sum of the numbers in set Y. (2) The median of the numbers in set Y is 0.

Isn't there really just one possibility for both sets, the one in which the median is 0? I can't think of two sets with those properties that have the same sum other than the one with median 0.

Re: Set X consists of seven consecutive integers... [#permalink]
03 Mar 2012, 06:10

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Expert's post

Set X consists of seven consecutive integers, and set Y consists of nine consecutive integers. Is the median of the numbers in set X equal to the median of the numbers in set Y?

Sets X and Y are evenly spaced. In any evenly spaced set (aka arithmetic progression): (mean) = (median) = (the average of the first and the last terms) and (the sum of the elements) = (the mean) * (# of elements).

So the question asks whether (mean of X) = (mean of Y)?

(1) The sum of the numbers in set X is equal to the sum of the numbers in set Y --> 7*(mean of X) = 9* (mean of Y) --> answer to the question will be YES in case (mean of X) = (mean of Y) = 0 and will be NO in all other cases (for example (mean of X) =9 and (mean of Y) = 7). Not sufficient. For example consider following two sets: Set X: {6, 7, 8, 9, 10, 11, 12} --> sum 63; Set Y: {3, 4, 5, 6, 7, 8, 9, 10, 11} --> sum 63.

(2) The median of the numbers in set Y is 0 --> (mean of Y) = 0, insufficient as we know nothing about the mean of X, which may or may not be zero.

(1)+(2) Since from (2) (mean of Y) = 0 and from (2) 7*(mean of X) = 9* (mean of Y) then (mean of X) = 0. Sufficient.

Set X consists of seven consecutive integers [#permalink]
02 May 2012, 07:47

Set X consists of seven consecutive integers, and set Y consists of nine consecutive integers. Is the median of the numbers in set X equal to the median of the numbers in set Y ? (1) The sum of the numbers in set X is equal to the sum of the numbers in set Y. (2) The median of the numbers in set Y is 0.

In retaltion to the clue (1), I have the following doubt: Algebraicaly, we can express the question in this way: X = {x, x+1, x+2,...x+6} Y = {y, y+1, y+2,...., y+8} Being x and y integers.

Based on the clue (1) that the sum of the numbers in set X is equal to the sum of the numbers in set Y, we can say:

7x + 21 = 9y + 36 7x - 9y = 15

Picking numbers I have found two possible combinations: x = -3 and y = -4, which means YES to the question. x = -12 and y = -11, which means NO to the question.

Re: Set X consists of seven consecutive integers [#permalink]
02 May 2012, 08:11

Expert's post

metallicafan wrote:

Set X consists of seven consecutive integers, and set Y consists of nine consecutive integers. Is the median of the numbers in set X equal to the median of the numbers in set Y ? (1) The sum of the numbers in set X is equal to the sum of the numbers in set Y. (2) The median of the numbers in set Y is 0.

In retaltion to the clue (1), I have the following doubt: Algebraicaly, we can express the question in this way: X = {x, x+1, x+2,...x+6} Y = {y, y+1, y+2,...., y+8} Being x and y integers.

Based on the clue (1) that the sum of the numbers in set X is equal to the sum of the numbers in set Y, we can say:

7x + 21 = 9y + 36 7x - 9y = 15

Picking numbers I have found two possible combinations: x = -3 and y = -4, which means YES to the question. x = -12 and y = -11, which means NO to the question.

Re: Set X consists of seven consecutive integers, and Set Y [#permalink]
04 Jun 2013, 02:38

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This post received KUDOS

Set X consists of seven consecutive integers, and set Y consists of nine consecutive integers. Is the median of the numbers in set X equal to the median of the numbers in set Y ? (1) The sum of the numbers in set X is equal to the sum of the numbers in set Y. (2) The median of the numbers in set Y is 0.

Quite tricky question. In such questions i try to answer YES or NO precisely by using the info from one of the statements. Lets try YES - two medians are equal, considering that both sets consists of consequtive integers, this to happen all number of set X should be within the set Y and then the mid number will be the same. Since there are no restrictions lets take numbers from 1 to 7 for set X and 1 to 9 for set Y - mid muber is 5.

Statement 1) from the first glance this condition does not fit into our sets from 1 to 9 and 1 to 7. So this statemnt seems sufficient, and i am about to say that possible answer for this question is either A or D. But then i am looking at the statement 2.

Statement 2) sometimes it helps to look at both statements before making any kind of conclusion because in real GMAT questions both statements never contradict each other, and by knowing more information it is easier to make final conclusion. In this qestion i forgot to consider that negative numbers also could be within the sets. This statement tells us about set y only, no info about set X - not sufficient.

Combining both statements: from st.1 we see that sum of set Y is 0, by st.1 we see that the sum of the set X also should be 0. This is only possible if the middle number of the set X is 0.

Answer is C

_________________

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gmatclubot

Re: Set X consists of seven consecutive integers, and Set Y
[#permalink]
04 Jun 2013, 02:38