Given the following speed in radar below,

To find the first quartile, Q₁ below, where N = 12

Hence, Q₁ = 68
To find the second quartile, Q₂, where N = 12,

Since the median lies between the 6th and 7th data, hence Q₂ is,

Hence, Q₂ = 73.5
To find the third quartile, Q₃, where N = 12,

Hence, Q₃ = 88
To find the Interquartile range (IQR),

Hence, IQR = 20