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: B
The given numbers form an arithmetic progression. In an A.P., the mean is equal to the middle term. Here, there are 5 terms, so the middle term is the 3rd term, which is x+4.
Given that the mean is 11, we have x + 4 = 11, which gives x = 7.
The five numbers are: 7, 9, 11, 13, 15.
The last three observations are 11, 13, and 15.
The mean of these three numbers is \(\frac{11+13+15}{3} = \frac{39}{3} = 13\).