As can be seen from the problem, the length of the rectangle has increased by one third, and it must have
12× (1+1/3) =16 decimeter.
Let the changed width be y decimeter. If the area is constant, the equation can be obtained.
16y= 12x
Pursue simplification
y=75%x
The width is reduced by 25%.
A: The width should be reduced by 25%.
Analysis: This question can find out the equivalence relationship by setting unknown numbers, thus listing the equations. This method can simplify the problem and make it difficult. You will often use the idea of this equation in junior high school. 、
2 solution: it is easy to know from the meaning of the question that the height of the cone is the length of a cube, that is, 6 cm.
The diameter of the bottom of the cone is the length of the cube, that is, 6 cm. The radius is 3 cm.
The cone volume formula is
V= 1/3(Sh) (Note: V is the volume, S is the bottom area, and H is the height. )
Then v =1/3× (3× 3 π× 6) =18 π ≈ 56.52 cubic centimeters.
The maximum volume is 56.52 cubic centimeters.
Solution: After sawing for six times, there should be seven sections. The length of a short segment is 5÷7 = 5/7÷≈0.7cm.
In fact, sawing into two parts only takes once and takes two minutes. Then it takes 12 minutes to saw six times.
Answer: Each paragraph is about 0.7㎝, and the time is 12 minutes.
Analysis: This is a simple "tree planting problem". For example, in a street with a length of 10 meter, if trees are planted at the beginning and end, plant one every 2 meters to find the number of trees. The answer to this question is six strains. 10÷2+ 1=6。
These problems are slightly higher on the basis. But as long as you broaden your mind and are willing to study hard, you will certainly achieve ideal results in mathematics!
One day, I will ride the wind and waves, raise the Yun Fan and cross the sea.