inter77Disabled Vehicle: SB on I-81 at MM82.2 (0.5mi north of I-77 Exit81) in Wythe Co. No lanes closed. 7:12PM. I-77 Virginia Road Conditions.An Example of Calculating IQR Using an IQR Formula. To identify the interquartile range of a set of data, simply subtract the first quartile from the third quartile as follows: