GMAT Prep Test 2

dsuna · Posted: Sun Mar 25, 2007 10:26 am Post subject: GMAT Prep Test 2

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

jayhawk2001 · Posted: Sun Mar 25, 2007 1:07 pm Post subject:

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.