If the mean of the observations x, x + 4, x + 5, x + 7, x + 9 is 9, then the mean of the last three observations is :
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Correct answer: C
Explanation
The correct answer is option 3 i.e. 11
Mean = Sum of all observation / number of observation.
9 = x + x+4 + x+5 + x+7 + x+9 /5
9 = 5x + 25 / 5
5x + 25 = 45
x = 20/5 or 4
The mean of the last three observations = x+5 + x+7 + x+9 / 3
9 + 11 + 13 / 3
⇒ 33/3 = 11