Question

If the mean of five observations x, x+2, x+4, x+6, x+8, is 11, then the mean of first three observations is
A. 9
B. 11
C. 13
D. none of these

Answer 1

Given : Mean of five observations x, x + 2, x + 4, x + 6, x + 8, is 11

Total number of all observations = 5

Mean = Sum of all the observations/Total number of observations

11 = (x + x + 2 + x + 4 +  x + 6 + x + 8)/5

11 × 5   = (5 x + 20)

55 = (5 x + 20)

5x = 55 - 20

5x = 35  

x = 35/5  

x = 7

First observation = x = 7

Second observation = x + 2 = 7 + 2 = 9

Third observation = x + 4 = 7 + 4 = 11

Mean of first three observations = (7 + 9 + 11)/3 = 27/3 = 9  

Hence, Mean of first three observations is 9.

Option (A) 9 is correct.

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