Question

if the mean of five observations x , x+2 , x+4 , x+6 , x+8 is 11 find the mean of first three observation.

Answer 1

x+x+2+x+4+x+6+x+8/5=11
5x+20/5=11
5x+20=55
5x=35
x=7
first three observations are x,x+2,x+4=7,9,11
7+9+11/3=27/3=9
Therefore the  mean of first three numbers is 9

Answer 2

given : the mean of the first five observations - x, x+2, x+4, x+6, x+8 is 11 required to find out : the first three observations
solution : 
x + x+2 + x+4 + x+6 + x+8 / 5 = 11         
5x + 20 / 5 = 11
5x + 20 = 11*55
5x + 20 = 55
5x = 55 - 20
5x = 35  
x = 35/5
∴ x = 7
the first three observations -
x = 7
x+2 = 7+2 = 9
x+4 = 7+4 = 11
∴ the first three observations are 7, 9, 11
the mean of the first three observations :
 -> 7+9+11/3
->27/3 
∴ 9 is the mean of the first three observations
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