Question
If average of 20 observations x1,x2, ....., x20 is y, then the average of x1 – 101, x2 – 101, x3 –101, ....., x20 –101 is
Answer: Option B Answer: (b)
${X_1 + X_2 + X_3 + X_4 + ..... + X_20}/20 = Y$
$X_1 + X_2 + X_3 + X_4 + ..... + X_20 = 20Y$
$= {X_1 - 101 + X_2 - 101 + X_3 - 101 + X_4 - 101 + ..... + X_20 - 101}/20$
$= (X_1 + X_2 + X_3 + X_4 + ..... + X_20) - 20 x 101/20$
$\text"20Y - 20 x 101"/20$
= Y - 101
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