(1) According to the histogram, the number of people who are "better" in this questionnaire survey is 100, and the number of people who are "better" after observing the statistical chart of the plate accounts for 50%.

Then the sample size is100 ÷ 50% = 200;

(2) The average number of people in the pie chart accounts for 1-25%-50%-5%=20%.

Central angle α = 360× 20% = 72;

(3) As the sample size is 200, the average population accounts for 20% and the poor population accounts for 5%.

So the average number of people is: 200×20%=40 (people), and the difference number is: 200×5%= 10 (people);

Supplementary pictures are as follows:

(4) Strengthening citizens' awareness of creating a sanitary city is the premise of improving the city appearance and environment.

So, the answer is: 200,72. Strengthening citizens' awareness of creating a sanitary city is the premise of improving the city appearance and environment.