If 65 is the range of the ungrouped data  $50,70,60,B,20,40$, then the absolute difference of the possible values of B is 

Given range = 65 and 50, 70, 60, B, 20, 40. B
may be either least value (or) greatest value.
$\begin{array}{rl} & \Rightarrow B-20=65\text{and}70-B=65\\ & \Rightarrow B=85\text{and}B=5\end{array}$
Now absolute difference of B values = 80