The outcome of each of 30 items was observed; 10 items gave an outcome −d each, 10 items gave outcome each and the remaining 10 items gave outcome +d each. If the variance of this outcome data is then d equals 

(a) 
2 
(b) 

(c) 
(d) 
The outcome of each of 30 items was observed; 10 items gave an outcome −d each, 10 items gave outcome each and the remaining 10 items gave outcome +d each. If the variance of this outcome data is then d equals 

(a) 
2 
(b) 

(c) 
(d) 
Variance is independent of origin. So we shift the given data by .
So, =
⇒d^{2}=2⇒d=