Mean-Max- Min functions for vectors

Hi everyone, 

I have this function that I used to find R from it 

Now I want to find the min, max and max  from it ..but didn't work . It tells me that the values should be scalar 

and when I do this , it gives me the same results of the original one not the average

I need to find the min, average , and max values

Thanks 

Yusra