Xiao Gang used to have some pictures. He took out half of them and gave them to his younger brother. Later he bought 18 more. At this time, there were 47 pictures. How many pictures did he have?

(47-18) × 2, = 29 × 2 = 58. A: he used to have 58 pictures

Xiao Ming is walking on the road at a speed of 6 km / h. a car with a body length of 20 meters comes from behind and passes by Xiao Ming. If it takes 1.5 seconds to pass by Xiao Ming, the speed of the car is ()
A. 54 km / h B. 60 km / h C. 72 km / h D. 66 km / h

Suppose the speed of the car is x km / h, then 1.53600x-6 × 1.53600 = 201000. The solution is: x = 54. A: the speed of the car is 54x km / h

Xiaolan and Xiaoli walk to school. Xiaolan walks 50 meters per minute and Xiaoli 45 meters per minute. Xiaolan is several percent faster than Xiaoli every minute, and Xiaoli is five percent faster than Xiaoli every minute
Xiaolan is a few percent slower

It is important to find the unit "1" and the unit "1" in this type of question
First question: how much faster is Xiaolan than Xiaoli per minute? "Xiaoli is behind the comparison, so the first unit is Xiaoli: 50-45 = 5,5 / 45 = 1 / 9 = 11.1%"
Second question: how much slower is Xiaoli than Xiaolan per minute? "Xiaolan is behind the comparison, so unit one is Xiaolan: 50-45 = 5,5 / 50 = 1 / 10 = 10%"

Mathematics problems (geometry problems about triangles in grade one of junior high school)
If ad is the middle line on the BC side of △ ABC, the area of △ abd is 6cm & sup2;, AC = 3cm, then the length of the height on the AC side of △ ABC is——————

∵ s △ abd = 1 / 2 s △ ABC
∴S△ABC＝2 S△ABD
＝2×6cm²
＝12cm²
Let the height of AC be, then:
BE＝（2 S△ABC）/AC
＝（2×12cm²）/3cm
＝ 8cm
The height on AC is 8cm

As shown in the figure, given the line segments a, B and C, (a > b > C), draw a line segment with a ruler (without scale) and a compass so that it is equal to A-B + 3C
If we know that the remainder of an angle is 1 ° more than 9 / 2 of its complement, we can find the degree of this angle

First, how do you do? Basic mechanical drawing
Second, let X be the degree of this angle
90-x=(180-x)*9/2+1--->x=206

Solving equations 3 (x-1) = y + 5 2 (y + 1) = x + 1 by addition subtraction elimination method

3(x-1)=y+5
2(y+1)=x+1
3x-3=y+5
2y+2=x+1
3x-y=8
x-2y=1
6x-2y=16①
x-2y=1②
① - 2 is 5x = 15
So x = 3
Substituting x = 3 into 2 gives 3-2y = 1
So y = 1
So the solution of the equations is x = 3, y = 1

In the equal ratio sequence {an}, if the common ratio q = 2 and the sum of the first 99 terms s99 = 30, then A3 + A6 + A9 + a99=______ ．

Because {an} is an equal ratio sequence with a common ratio of 2, let A3 + A6 + A9 + +A99 = x, then a1 + A4 + A7 + +a97=x4a2+a5+a8+… +a98=x2S99=30=（a1+a4+a7+… +a97）+（a2+a5+a6+… +a98）+（a3+a6+a9+… +a99）=x+x2+x4∴a3+a6+a9+… A99 = 1207, so the answer is: 1207

20 square decimeters 7 square centimeters = how many square centimeters 6080 cubic centimeters = () cubic decimeters () cubic centimeters
There is a rectangular ventilation pipe with a height of 2 mm, a width of 1.5 DM and a length of 3 dm
The surface area of a cuboid is reduced by () square decimeters, and the volume of the cuboid is () cubic decimeters
A cuboid of 5cm in length, 3cm in width and 2cm in height is made up of () cubes whose edges are 1cm in length
The two cold fields are 1 decimeter cube steel into a cross planting surface 5 cm long, 4 cm wide cuboid steel, the length of this steel is how many decimeters?

20 square decimeter 7 square centimeter = 2007 square centimeter 6080 cubic centimeter = (6) cubic decimeter (80) cubic centimeter to make one such ventilation pipe needs (2 + 1.5) x2x3 = 21 square decimeter, two are 2x21 = 42 square decimeter, the surface area reduces (2) square decimeter, the volume product of the assembled cuboid is (2) cubic decimeter

An automobile transportation company plans to use 20 vehicles to transport 36 tons of vegetables (a, B and C) to other places for sale (each vehicle is limited to be fully loaded, and can only carry the same kind of vegetables, and each vegetable is not less than one vehicle). How should the transportation make the company obtain the maximum profit? What is the maximum profit?
A, B and C
2.5 tons per vehicle
Profit per ton of vegetables

x. Y, Z, denote the number of vegetable carts of a, B and C respectively
W stands for profit
x+y+z==20
2*x+1*y+1.5*z==36
From the above two formula analysis of 13

How many tons is a cubic meter of earth rock?

Generally, the density of soil ranges from 2.6 to 2.8, and the average density of rocks on earth is about 3.8
In the earth rock, if there are more stones, the average density will be higher. If there are less stones, the average density will be lower. It should be between 2.5-3 tons. Therefore, a cubic meter of earth rock should be between 2.5-3 tons

Xiao Gang used to have some pictures. He took out half of them and gave them to his younger brother. Later he bought 18 more. At this time, there were 47 pictures. How many pictures did he have?