2. A rectangle with a length of 3 cm and a width of 2 cm rotates once around the width, and the volume of the obtained three-dimensional graph is (37.68 cubic centimeters).
3. The height of the cylinder is unchanged, the radius of the bottom surface is enlarged by 3 times and the volume is enlarged by 9 times.
4、 1/4= 1:4=2:(8 )=6÷( 12)=(0.25 )=(25 )%
5. Two fifths of (50) is 20kg, which is (25 )% more than 16kg.
10 kg is 25% more than (8) kg, and 30 kg is 25% less than 40 kg.
6. If y=3x, X and Y are in (positive) proportion, y=3/x, and X and Y are in (inverse) proportion.
7. if a=b(a, b≠0), then a: b = (1): (1)
8. On the map with the scale of 4: 1, the line segment of 8 cm represents the actual length of (2) cm.
9. Use four numbers (1, 2, 6, x) to form a proportion. The minimum value of x is (1/3) and the maximum value is (12).
10, a kind of sugar water, with sugar accounting for 10% and the weight ratio of sugar to water (1:9).
1 1.2/3 hours = (40) minutes 0.5 hectares = (5,000) square meters 5.07 cubic meters = (5,070) liters.
12.5 l = (5000) ml
3÷(40 )=7.5%=0.075= 15:(200 )=( 1.8 ):24
13, the original price of a dress 160 yuan, with a 30% discount. The current price is (1 12) yuan.
14, girls account for 40% of the class, boys are more than girls (50%), and girls are less than boys (33.3%).
15, number A is 80% of number B, number A is (20 )% less than number B, and number B is (25 )% more than number A.. ..
It is known that 16 and 1/3 of number A are equal to 1/2 of number B, so number B is 2/3 of number A. ..
17. Xiaoming buys books, and after a 20% discount, it is 16 yuan. He spent 4 yuan's money to buy this book.
18、
19. Add 8 to the previous item of 4:5. To keep the proportion unchanged, add (10) to the latter item.
20. Divide the 5-meter-long iron wire into 8 segments on average, with each segment being (5/8) meters long and each segment being (1/8) long.
2 1, a train 1/2 hours travels 40 kilometers, with an average of (80) kilometers per hour, and it takes (1/80) hours to travel1kilometer.
22. A batch of 500 pieces, 20 pieces failed the inspection, and the qualified rate was (96%).
23. The circumference of a circle is 6.28 decimeters, and the circumference of its semi-circle is (5. 14) decimeters.
24. (3): 8 = 3/4 = (3) ÷ (4) = (75)% = (0.75) (decimal)
25, know the object (horizontal) and (vertical), you can determine the position of the object.
26. For a project, it takes 12 hours for the apprentice to do it alone, and 8 hours for the master to do it alone. The efficiency ratio of apprentice to master is (2:3).
27. If 5y=4x, then X and Y are in (positive) proportion; If xy=8, then X is (inversely) proportional to Y;
If x+y = 4, then x and y are not proportional.
28. The sum of the sides of a cuboid is 72 decimeters, and the ratio of length, width and height is 3:2: 1. Its surface area is (198) square decimeter and its volume is (162) cubic decimeter.
29. The volume of water increases after freezing111,and the volume decreases after ice melts into water112.
30. 40% of 25 kg is _ _ _ 10 _ _ _ _ 35 kg is _ _ _ _ _ _ _ 75% of more than 20 kg.
40 tons increased by _ _ _ _ 12.5 _ _%, that is, 45 tons,100km, 25% more than _ _ _ 80 _ _%.
3 1, number A is 4/5 of number B, number A is 20 _ _ _% less than number B, and number B is 25 _ _ _ _% more than number A. 。
32. Cut a cylinder into the largest cone, the cut part is 12 cubic decimeter, and the volume of this cylinder is _ _ _ _18 cubic decimeter _ _ _.
33, two cylinders, the ratio of bottom radius is 2: 1, and the heights are equal, then its volume ratio is _ _ 4:1_ _ _.
34. 35 red flowers, yellow flowers 15, (35- 15) ÷ 15 means that there are many _ _ _ _ red flowers and yellow flowers.