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.