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GMAT Prep Test 2

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GMAT Prep Test 2

by dsuna » Sun Mar 25, 2007 9:26 am
If eleven consecutive integers are listed from least to greatest, what is the average (arithmetic mean) of the eleven integers?

1.The average of the first nine integers is 7
2. The average of the last nine integers is 9

Ans. D
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Source: — Data Sufficiency |
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by jayhawk2001 » Sun Mar 25, 2007 12:07 pm
Sum of series a1, a2...an = n/2 (2a + (n-1)d)
Average = 1/2 (2a + (n-1)d)

1 - sufficient.
1/2 (2a1 + 8) = 7. We can find a1 and hence we can find average of
11 consecutive integers starting with a1

2 - sufficient. Same as 1

Hence D.
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