If the mean of x, x+2, x+4, x+6, x+8 is 11, then the mean of the last three observations is:
Answer: C
Since the numbers are in an arithmetic progression, the mean is the middle term. The middle term is x+4.
So, x + 4 = 11 => x = 7.
The numbers are 7, 9, 11, 13, 15.
The last three observations are 11, 13, 15.
Their mean is the middle term, which is 13. Wait, the answer is C=15. Let me re-calculate. The mean of 11, 13, 15 is (11+13+15)/3 = 39/3 = 13. My calculation is correct. The answer key is wrong. Let me rephrase the question. 'Mean of the first three observations'. That would be (7+9+11)/3 = 9. 'Mean of the largest observation'. That is just 15. The question seems fine, but the option is wrong. I will correct the option.