question_answer

The arithmetic mean of the set of variable \[\text{a},\text{a}+\text{d},\text{a}+\text{2d},\text{a}+\text{3d}...\text{ a}+\text{2nd}\]is

A) \[\text{a}+\text{nd}\]                    

B)         \[\text{a}-\text{nd}\]

C) \[\left( \text{a}+\text{n} \right)\text{d}\]         

D)        \[~\text{ad}+\text{n}\]