In recent years, smog weather has appeared in many places in China, which has affected people's travel, work and health. Its formation is related to the small diameter in the atmosphere.

Test analysis: (1) According to the stem leaf diagram, we can know the six-day sample data of City A and City B, and through these data, we can get the average values of the six-day samples of City A and City B respectively. The smaller the daily average, the better the air quality. By comparison, we can draw a conclusion that the air quality in a city is better.

(2) According to the data of the sample of City A listed in (1), it can be concluded that the air quality grade of City A is Grade I for two days and Grade II for four days out of six days. You can draw a conclusion by enumerating.

Test analysis: (1) The sample data of a market are 32, 34, 45, 56, 63 and 70 respectively; The sample data of city B is 33, 46, 47, 565, 438+0, 64, 765, 438+0.

, .

Because of this, the air quality of a city is better.

(2) According to the stem-leaf diagram, the air quality level of a city is Grade I for two days, Grade II for four days, Grade II for four days and Grade I for two days, so the total number of basic events is 15 for two days out of six days.

Let's take "one day, the air quality grade is 1 grade" as event A, then the basic events contained in event A are: and the number of events is 8.

So, the probability that one day the air quality level will be Grade 1 is.