I. Concept

1 fill in the blanks

(1) Class 6 (1) has 20 boys and 25 girls. The number of boys is 80% of that of girls, and the number of girls is more than that of boys (25%).

(2) Because 10×9=6× 15, 6: 10 = (9): (5). ( 10):( 15)=6:9

(3) What are the cross sections after cutting?

Circular rectangular triangle

(4) Wang Wei earned 4080 yuan last month. Deduct 3,500 yuan, and pay personal income tax at the rate of 5%, with the tax payable (29 yuan).

(5) The height of two cylinders is equal, the ratio of bottom radius is 2:3, the ratio of bottom radius of two cylinders is (4:9), the ratio of side area is (2:3), and the ratio of volume is (4: 3).