Median of X-ray dosages in Exercise 25

Data from Exercises 25 of Exercises 22.1

Use the following data. The dosage (in mR) given by a particular X-ray machine was measured 20 times, with the following readings:

4.25, 4.36, 3.96, 4.21, 4.44, 3.83, 4.37, 4.27, 4.33, 4.34,
4.15, 3.90, 4.41, 4.51, 4.18, 4.26, 4.29, 4.09, 4.36, 4.23

Using the class limits 3.80, 3.90, 4.00, . . . , 4.60, construct a frequency histogram of these data.