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DS : Numbers 1

Expert replies
by Mission2012 » Wed Aug 28, 2013 7:37 am
If N different positive integers are added and the sum is denoted as S, and if S=NX, is X an integer?

(1) N is odd.

(2) All N numbers are consecutive integers.
If you find my post useful -> please click on "Thanks"
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Source: — Problem Solving |

by vinay1983 » Wed Aug 28, 2013 7:50 am
Statement 1: N is odd

3, 5, 7 If consecutive integers are taken

1+2+3=6=S 1+2+5+8+7=23=S 23=5X X not a integer

So S=3X i.e 6=3X
X=2

N=5 1+2+3+4+5=15 S=NX 15=5X X=5

If suppose the following numbers are taken(since statement 1 does not say anything about the sequence of the numbers)

S=1+2+4=7 N =3 7=3X X is not a integer
Statement 2
Suppose N=2

Then 1+2=3

S=3 N =2
So X=1.5

N=3

1+2+3=6=S 6=3X X=2

Not sufficient

Combine

Numbers are odd and in sequence

1+2+3=6=S N=3 6=3X X=2

1+2+3+4+5=15 N=5 15=5X X=3

1+2+3+4+5+6+7=28 N=7 28=7X X=4

OA C

I hope I am correct!
You can, for example never foretell what any one man will do, but you can say with precision what an average number will be up to!
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by [email protected] » Wed Aug 28, 2013 11:50 am
Hi vinay1983,

Your solution is correct; nicely proven!

This question hides an important number property rule involving consecutive integers: When dealing with an ODD number of CONSECUTIVE integers, the average is ALWAYS equal to the "middle" term. The wording of this prompt essentially asks you if the average of a group of numbers is an integer, so this rule applies.

GMAT assassins aren't born, they're made,
Rich
Contact Rich at [email protected]
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by vinay1983 » Wed Aug 28, 2013 9:28 pm
[email protected] wrote:Hi vinay1983,

Your solution is correct; nicely proven!

This question hides an important number property rule involving consecutive integers: When dealing with an ODD number of CONSECUTIVE integers, the average is ALWAYS equal to the "middle" term. The wording of this prompt essentially asks you if the average of a group of numbers is an integer, so this rule applies.

GMAT assassins aren't born, they're made,
Rich

Thanks a lot Rich.You see this is the 1st problem I have solved correctly in this forum on my own reasoning.

I now know that if I apply my mind I can BEAT THE GMAT!
You can, for example never foretell what any one man will do, but you can say with precision what an average number will be up to!
Join the discussion