There are 20 boys and 25 girls in the six-year (1) class. (1) what percentage of boys is girls? (2) what percentage of girls is boys? (3) What is the percentage of boys in the class? (4) what is the percentage of girls in the class?

There are 20 boys and 25 girls in the six-year (1) class. (1) what percentage of boys is girls? (2) what percentage of girls is boys? (3) What is the percentage of boys in the class? (4) what is the percentage of girls in the class?

（1）20/25=.08=80%
（2）25/20=1.25=125%
（3）20/（20+25）=0.445=44.4%
（4）25/（20+25）=0.556=55.6%
A:
Note: it is a division sign, and (3) (4) is used to reserve three decimal places
(1) What percentage of boys is girls?
20÷25=0.8=80%
(2) What's the percentage of girls compared with boys?
25÷20=125%
(3) What percentage of the class are boys?
20÷（20+25）=20÷45=44.4%
(4) What percentage of the class are girls?
25÷（20+25）=25÷45=55.5%
（1）20/25*100％=80％
（2）25/20=5/4
A: the number of male students is 80% of that of female students, and the number of female students is 5 / 4 of that of male students
（1）20÷25=80%
（2）25÷20=125%
（3）20÷（20+25）≈44。 4%
（4）25÷（20+25）≈55.6%
1.﹙20/25﹚×100％=80％
2.25/20=5/4
3.100％×20/﹙20+25﹚≈44.4％
4.100％×25/﹙20+25﹚≈55.5％
【1】 20 △ 25 = 25 / 20 (approximately) = 5 / 4
【2】 25 △ 20 = 20 / 25 (approximately) = 4 / 5
【3】 20 ÷ (20 + 25) = 45 / 20 (approximately) = 4 / 9
【4】 25 ÷ (20 + 25) = 45 out of 25 (approximately) = 5 out of 9
Simplification of trigonometric function cos2a divided by Tan (π + a)
Cos 2A divided by Tan (π + a)
=cos2A/sinA
There seems to be no need to simplify
If you don't ask, I'll have to change it to the ground floor
According to you, this is not simplification, it's identical deformation
So, you have to give us goals
PS: it is suggested that after you revise the question in the future, you should ask as much as possible, otherwise, it will be difficult for the respondent to see it
To detailed process, thank you, by the way to guide the simplification of this problem skills, good points. Supplementary question: (= cos (2a) / [2cot (π / 2 - (π / 4-A)) sin2 (π / 4 + a)] = cos (2a)/[
tan（π+A）=tanA
cos2A=（cosA）^2-(sinA)^2
cos2A/tan(π+A)
=[（cosA）^2-（sinA）^2]/tanA
=(cosA)^3/sinA-sinAcosA
There are 25 boys and 20 girls in class 3 of grade 5. What percentage of boys are girls? What percentage of the class are girls?
Answer: boys are 54% of girls, girls are 49% of the class
Given Tan (α + π / 4) = - 1 / 7, α∈ (π / 2, π), find Tan α + (cos2a + 1) / [√ 2cos (α - π / 4) - sin2a]
Tan (α + π / 4) = - 1 / 7, α∈ (π / 2, π) Tan (α + π / 4) = (Tan α + Tan π / 4) / (1-tan α, Tan π / 4) = (Tan α + 1) / (1-tan α) = - 1 / 77tan α + 7 = - 1 + Tan α, Tan α = - 4 / 3 α∈ (π / 2, π) cos α = - 1 / radical (1 + Tan ^ 2 α) = - 1 /
There are 28 boys and 26 girls in class 51. What is the proportion of girls and boys in the class? What is the proportion of girls to boys?
The total number of students in the class is 28 + 26 = 54
Girls account for 26 / 54 = 13 / 27 of the class
Boys account for 28 / 54 = 14 / 27 of the class
Girls are 26 / 28 of boys = 13 / 14
It is known that Tan α = √ 2 / 2, Cos2 (π - α) + sin (π + α) cos (π - α) + 2sin2 (α - π) needs detailed process~
The solution is Cos2 (π - α) + sin (π + α) cos (π - α) + 2sin2 (α - π) = cos (2 π - 2 α) + [- sin (α)] [- cos (α)] + 2Sin (2 α - 2 π) = Cos2 α + sin (α) cos (α) - 2Sin (2 π - 2 α) = Cos2 α + sin (α) cos (α) - 2Sin (- 2 α) = Cos2 α + 1 / 2 * 2 * sin (α) cos (α) + 2Sin (2
There are 58 boys and girls in a class. One fourth of the boys are 2 more than one sixth of the girls. How many boys are there?
2. Simple calculation: 2004 9 × 2003 9
3. A and B vehicles leave from the East and West stations at the same time, and meet at 5km from the midpoint. It is known that the speed of a vehicle is 75% of that of B vehicle. How many kilometers is the distance between the East and West stations?
1. Set the number of boys as X and the number of girls as y
X + y = 58 ① 1 / 4x-2 = 1 / 6y ② x = 28 y = 30
So there are 28 boys and 30 girls
3. The speed ratio of a and B vehicles is 3:4 (75%)
5 * 2 / (4-3) = 10 hours
10 * (3 + 4) = 70 km
Simplifying cos π / 7 * Cos2 π / 7 * Cos4 π / 7
Tip: according to the analysis, double angle formula should be used
cos（π/7）*cos（2π/7）*cos（4π/7）
=[2sin(π/7)cos（π/7）*cos（2π/7）*cos（4π/7）]/2sin(π/7)
=[sin(2π/7)*cos（2π/7）*cos（4π/7）]/2sin(π/7)
=[2sin(2π/7)*cos（2π/7）*cos（4π/7）]/4sin(π/7)
=[sin(4π/7)*cos(4π/7)]/4sin(π/7)
=[2sin(4π/7)*cos(4π/7)]/8sin(π/7)
=Sin (8 π / 7) / 8sin (π / 7) (because sin (8 π / 7) = - sin (π / 7))
=-1/8
There are 58 students in a class, including 26 boys and 32 girls. What percentage of the class are boys and girls
13 out of 29 boys and 16 out of 29 girls
It is proved that Cos2 α + Cos2 β = 2cos (α + β) cos (α - β)
Proof: the left side of the equation = Cos2 α + Cos2 β
=cos[(α+β)+(α-β)] + cos[(α+β)-(α-β)]
=cos(α+β)cos(α-β) - sin(α+β)sin(α-β) + cos(α+β)cos(α-β) + sin(α+β)sin(α-β)
=2cos(α+β)cos(α-β)
=On the right side of the equation
It can be proved by sin2x + sin2y = 2Sin (x + y) cos (X-Y)
cos2α+cos2β=sin（π/2-2α）+sin（π/2-2β）
=2sin(π/2-α-β)cos(β-α)
=2cos(α+β)cos(α-β)
According to the formula of cos α · cos β = (1 / 2) [cos (α + β) + cos (α - β)]
Let α + β = a, α - β = B, that is, a + B = (α + β) + (α - β) = 2 α, A-B = (α + β) - (α - β) = 2 β
cos2α+cos2β=cos(A+B)+cos（A-B）
According to Cosa · CoSb = (1 / 2) [cos (a + b) + cos (a-b)]
cos2α+cos2β=cos(A+B)+cos（A-B）=2cosA·cosB=2cos(α+β)cos(α-β)