1, equivalent area = square length ×5+ square length ×5+5×2.

Therefore, the side length of a square =(66-5×2)÷(5+2)=8cm.

Rectangular area =8×8+66= 130 cm2.

After 2.30kg of bucket A is poured out, bucket A and bucket B = 180-30 = 150kg, which is 4+ 1=5 times that of bucket A. ..

So, the result is that a barrel has: (180-30) ÷ (4+1)+30 = 60 kg.

Originally, barrel B had: 180-60 = 120kg.

3. The total number remains unchanged.

At first, it was 3/(7+3)=3/ 10 of the total number of participants.

Later it was 2/(2+3)= 2/5 of the total population.

So the total number of people =30÷(2/5-3/ 10)=300.