The Environmental Protection Agency (EPA) monitors air quality in various areas around the country. It uses an Air Quality Index to report conditions on a scale of 1 to 200. Based on its December database, the EPA published index values (covering 273 days of observation) for the Los Angeles-Long Beach area of California: 

a. Draw the frequency histogram for the data.

b. Use the grouped data table to approximate the mean, the variance and the standard deviation of the air quality index values.

Transcribed Image Text:

Index Value 0 to under 50 50 to under 100 100 to under 150 150 to 200 Interval Midpoint 25 75 125 175 No. of Days 74 58 24 Total 273