In Data Set 5 in Appendix B, blood lead levels are represented as 1 for low, 2

Question:

In Data Set 5 in Appendix B, blood lead levels are represented as 1 for low, 2 for medium, and 3 for high. The average (mean) of the 121 blood lead levels is 1.53.
Identify the level of measurement of the data. Also, explain what is wrong with the given calculation.