2. Analysis: Ribbons are tied in a cross shape, and the length of ribbons (except knots) is equal to the sum of the perimeters of a rectangle (front view) with a length of 30cm and a width of 25cm, that is, 2 * (30+25)+2 * (20+25) = 200cm. Considering that the length of the ribbon used is affected by the tightness of binding, it is more reasonable to choose 23 decimeters.

Answer: c

3. Analysis: Since neither X nor Y is 0, the original formula can be transformed into xy = k+2; When K is constant, k+2 is constant, and solid X and Y are inversely proportional.

Answer: b

9. Analysis: The difference between the distances traveled by car B in 10 (scenario 1) and 10 (scenario 2) is the distance traveled by car B in 10 minutes. According to the distance relationship between car B and car A in scene 1 and scene 2, we can solve this problem by making equations.

Solution: Assume that the driving time of A before 10 is t, the driving speed is v, both T and V are greater than 0, and the speeds of A and B are the same. According to the meaning of the question, the equation can be listed as: vt/3+10v = (t+10) v/2, which can be simplified as tv/6=5v.

1 1. Analysis: According to the meaning of the question, the efficiencies of A, B and C are 1/6, 1/7,114 respectively. If Party C helps Party A for x hours and Party B for y hours, there will be (x+y)

Answer:1.75; 3.5

16. analysis: suppose point a in the figure falls on point a' after folding, because the length of the paper will not change after folding, A'B=AB, A'D=AD. It can be seen that the perimeter of the shaded part in the figure is actually equal to the perimeter of the rectangle, that is, 2 * (5+2.4) =14.8cm..

Answer: 14.8

Analysis: The volume formula of cone is: V=Sh/3, the volume formula of cylinder is: V=Sh, s is the bottom area, the current bottom area s is the same, and the ratio of volume V is 1:6, so the ratio of height H should be 1:2.

Answer: 8.4

4. Analysis: When the cylinder is cut and spliced into approximate cuboids with the same height, the increased surface area is actually the cross-sectional area of the cylinder diameter. If we know the height of the cylinder and the increased surface area, we can get the diameter of the cylinder bottom, and then we can get the volume of the cylinder.

Solution: Cylinder bottom diameter d = s/h =120/(3 *10) = 4cm; The cylinder volume v = π * (d/2) 2 * h = 376.8 square centimeters (π is 3. 14).

. √

5.775 km

6.567

7.32.4

*8.6.36 (Note: According to the diagram, the area of triangle DCE cannot be greater than that of triangle BCD, and the title is incorrect. The calculation result is obtained by exchanging the positions of b and e. )

The order of answering questions is from left to right and from top to bottom; Go to dinner and continue later. ...