Question

If the mean of 5 observations x, x+2, x+4, x+6 and x+8 is 11, the mean of the last 3 observations is

Answer 1

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Here is your answer.
As we know the formula

Mean = Sum of Observations/Total Observations
$11 = \frac{x + x + 2 + x + 4 + x + 6 + x + 8}{5} \\ 11 \times 5 = 5x + 20 \\ 5x = 55 - 20 \\ 5x = 35 \\ x = 7$
So Last three Observations is
7+4 = 11
7+6 = 13
7+8 = 15

Now
Mean of Last three Observations is
$= \frac{11 + 13 + 15}{3} \\ = \frac{39}{3} \\ = 13$

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