let n-5, n-4, n-3, n-2, n-1, n, n+1, n+2, n+3, n+4, n+5 be the 11 consecutive numbers. The average of these numbers is n. Then the question can be rephrased to 'What is the value of n?'
1) Average of the 1st nine integers is 7
Average of the first 9 integers n-5, n-4, n-3, n-2, n-1, n, n+1, n+2, n+3 is n-1 = 7. So, the value of n is 8. Statement I alone is sufficient to answer the question.
2) Average of last 9 integers is 9
Average of the last 9 integers n-3, n-2, n-1, n, n+1, n+2, n+3, n+4, n+5 is n+1 = 9. So, the value of n is 8. Statement II alone is sufficient to answer the question.
Option
D is the right choice!
