There are 45 steel pipes in the factory to be stacked into trapezoid, and after stacking, the upper layer is 7, and the number of layers is only 5? Determinant

Let X be the lowest root
Because each layer has to decrease by one
Then the fifth layer needs to subtract 4
x-4=7
x=11
I'm a teacher. Thank you

RELATED INFORMATIONS

1. Xiao Li sees a pile of steel pipes in the warehouse. There are 15 steel pipes at the bottom layer. There is one difference between each two adjacent layers. There are 8 steel pipes at the top layer. How many steel pipes are there in this pile?
2. How to calculate the number of stacked logs? For example, a pile of wood is placed in a trapezoidal shape. There are four pieces in the bottom layer, and then every time it goes up, there will be more than one piece in the upper layer. If there are seven layers, how can I calculate the number of pieces in this pile of wood?
3. Some of the logs are triangles, and the bottom layer is 120. How many logs are there in this pile? Please explain it to me,
4. A pile of wood, stacked into a trapezoid, the lower layer stacked 12, the upper layer stacked 5, a total of 8 layers stacked, a total of several?
5. The wood of a timber factory is piled into a triangle shape with a cross section. There are 12 layers, one in the top layer and 12 in the bottom layer. How many are there in this pile Question: the wood of a timber factory is piled into a triangle shape with a cross section. There are 12 layers, one in the top layer and 12 in the bottom layer. How many pieces are there in this pile?
6. There is a pile of wood piled into a triangle. There are 145 pieces in the bottom layer. Do you know how many pieces there are in total
7. There are three pipes with radius of 0.5m on a construction site. As shown in the figure, how high is the top of the pipe from the ground? What about six in three? How about 10 in four layers?
8. There are three pipes with radius of 0.5m on a construction site. As shown in the figure, how high is the top of the pipe from the ground? What about six in three? How about 10 in four layers?
9. The diameter of the cylindrical pipe for transporting concrete in construction site is 16 cm. The velocity of concrete in the pipe is 35 meters per minute. It takes 10 minutes to transport a truck. What is the volume of concrete in a truck? (the number obtained keeps the whole number)
10. The diameter of the cylindrical pipe for transporting concrete in construction site is 16 cm. The velocity of concrete in the pipe is 35 meters per minute. It takes 10 minutes to transport a truck. What is the volume of concrete in a truck? (the number obtained keeps the whole number)
11. A total of 465 steel pipes are placed on a V-shaped frame, one on the bottom layer and one more on each upper layer. How many layers are there? How many on the top layer?
12. Pile up a pile of steel pipes, 11 at the bottom, one less at each layer upward, until one. How many steel pipes are there in this pile?
13. Uncle Li's average step length is about 70cm. He walked around the edge of a rectangle which is twice the length and width. He just walked 900 steps?
14. Xiaohua walked three times on the 60 meter track, 119 steps in the first time, 118 steps in the second time and 123 steps in the third time. How many meters is Xiaohua's average step length? He walked 1500 steps from home to school. How many meters is it from Xiaohua's home to school?
15. Xiaoguang walked 80 meters, 125 steps for the first time, 130 steps for the second time, 123 steps for the third time and 122 steps for the fourth time. His average step length was () meters?
16. Xiao Ming wanted to know his step length, so he walked three times along the track 100 meters away, 124, 126 and 125 steps respectively. Xiao Ming's step length was about 100 meters______ He measured the length of the cement road in the center of our school. After about 150 steps, the cement road in the center is about long______ Rice
17. A and B run back and forth on a 100 meter long straight road, with a speed of 3 meters per second and B speed of 2 meters per second. If they start from both ends of the straight road at the same time, how many times do they meet after 10 minutes?
18. Xiao Ming walked along a 70 meter straight road. He took 110 steps for the first time, 111 steps for the second time, 109 steps for the third time and 110 steps for the fourth time. What is the average length of one step
19. Sasa walked three times along the 80 meter long straight road, 120 steps in the first time, 124 steps in the second time, and 122 steps in the third time. What is the average length of Sasa's step She walked 1020 steps from home to school. How many meters does Sasha's home go to school?
20. Xiao Ming walked four times along a 50 meter long straight road, 78 steps for the first time, 82 steps for the second time, and 79 steps for the third time, The fourth time is 80 steps. Xiaoming's average step length is about () meters. The number is two decimal places