Three good students account for 18% of the total number of students in the class, three good students and the proportion of the total number of students in the class is______ ．

Three good students account for 18% of the total number of students in the class, three good students and the proportion of the total number of students in the class is______ ．

Three good students account for 18% of the class, and the ratio of three good students to the class is 1:8

Divide the whole class into five groups on average. What is the number of students in one group? What is the number of students in four groups?

Divide the whole class into five groups, one group is 1 / 5 of the total number of the class, four groups are 4 / 5 of the total number of the class

The number of boys in a class is 5 less than that of the whole class, and the number of girls is 2 less than that of boys
fast
speak

Method: the most intuitive
Set the class size as X
(5/8)x-5+(5/8)x-5-2=x
x=48
Method 2: you need to use your brain
There are x boys
x+5/(2x-2)=5/8
X = 25, so the class is 2x-2 = 48

As shown in the figure, the elevation angle of C is ∠ CAD = 30 ° from a, the elevation angle of C is ∠ CBD = 45 ° from B, and the angle of view is ∠ ACB when measuring a and B from C=______ Degree

Method 1: ∵ - CBD is the outer angle of △ ABC, ∵ - CBD = ∵ CAD + ∵ ACB, ∵ - ACB = ∵ CBD - ∵ ACB = 45 ° - 30 ° = 15 °. Method 2: from the definition of adjacent complementary angle, ∵ - CBD = 180 ° - 45 ° = 135 °. ∵ - CAD = 30 °, ∵ CBA = 135 °, ∵ - ACB = 180 ° - CAD - ∵ CBA = 180 ° - 30 ° - 135 ° = 180 ° - 165 ° = 15 °

40+□×3=100．

If we regard □ as an unknown number x, the original formula becomes 40 + 3x = 100, & nbsp; & nbsp; 3x = 60, & nbsp; & nbsp; & nbsp; X = 20

The length of the rectangle is 100 meters and the width is 80 meters. How many square meters is the area if the length and width of the rectangle are increased by 20 meters?
How many square meters is the area increased?

Add (100 + 80) * 20 + 20 ^ 2 = 4000

From the image C translation vector a =? Of X-1 under the function y = root, the image C1 of X under the function y = root is obtained, and then from the C translation vector b = (2, - 1), the function analytical expression of image C2 is?

a=（-1,0）
C2: y = under radical (x-3) - 1

Compare the size of a & # 178; + 1 and a & # 178; - 1; 2x-1 and X + 2 with the difference method

(a²+1)-(a²-1)
=a²+1-a²+1
=2>0
So: A & # 178; + 1 > A & # 178; - 1
(2x-1)-(x+2)
=2x-1-x-2
=x-3
discuss
(1) When X. > 3. X-3 > 0
In this case, 2x-1 > x + 2
(2) When x = 3, x-3 = 0
In this case, 2x-1 = x + 2
（3）
When x

As shown in the figure, the slope (slope ratio) of slope AC is 1:3, AC = 10m. There is a flagpole BC at the top of the slope. There is a color band AB connecting point B and point a at the top of the flagpole, ab = 14m. Try to find the height of flagpole BC

In RT △ AEC, AC = 10, from the slope ratio of 1:3, it can be seen that: CAE = 30 °, CE = AC · sin30 ° = 10 × 12 = 5, AE = AC · cos30 ° = 10 × 32 = 53. In RT △ Abe, be = AB2 − AE2 = 142 − (53) 2 = 11. ∵ be = BC + CE, ∵ BC = be-ce = 11-5 = 6 (m). Answer: the height of flag pole is 6m

How do we use plants

Plants, fruits and seeds as food; ecological effects of plants; extraction of drugs contained in plants; cultivation of sentiment as an ornamental