A manuscript has been typed for 400 words, and there are still four seventh of this manuscript. How many words are there in this manuscript

A manuscript has been typed for 400 words, and there are still four seventh of this manuscript. How many words are there in this manuscript

400 ÷ (4 / 1-7)
=400 △ 3 / 7
=2800 (words)

It takes mother 5 out of 8 hours to type a 4000 word document. How many words can she type in an hour?
To list

Four thousand ／ five eighths is equal to six thousand four hundred. It can type six thousand four hundred words in an hour

Ellipse x ^ 2 / 25 + y ^ 2 / 16 = 1 f right focus m (3.1), then PM + PF is the minimum

A = 5, let the left focus be e
∴PM+PF=2a-PE+PM
When e, m and P are collinear, pm-pe has minimum value
That is - | EM | and the EM length is d = √ 6 & # 178; + 1 & # 178; = √ 37
The minimum value of pm-pe is - √ 37
So the minimum value of PM + PF is 10 - √ 37

(20052005-2005.2005)/(80208020-8020.8020)
8.1*1.3-8/1+1.9*1.3+11.9/1.3

(20052005-2005.2005)÷(80208020-8020.8020) =2005*(10001-1.0001)÷[8020*(10001-1.0001) =2005÷8020 =1/48.1×1.3-8÷1.3+1.9×1.3+11.9÷1.3=(8.1+1.9)×1.3+(11.9-8)÷1.3=13-3=10

If the system of equations with X, y as unknowns {x square + y square = 16, X-Y = k has a real number solution, finding the range of curve value of K is a concrete process,

X square + y square = 16 is a circle with the origin as the center and 4 as the radius,
Therefore: the absolute value of X is greater than or equal to 0 and less than or equal to 4, so is y
Therefore, the absolute value of X-Y is greater than or equal to 0 and less than or equal to 4,
Therefore, K is greater than or equal to - 4 and less than or equal to + 4

Every day 20. Has the addition and subtraction mixed operation. Has a little difficulty

37+8-9=?15-58+12=?12+23= 14+21=?
65+18=?34+18=?23-14+59=?25-17+39=?
33-7+14=?13+9+7=?12+6+9=?13-68+74=?
78+68-45=?76+37-27=?23+45-12=?24-46+23=?
34+56-45=?54-12-23=?12+54-23=?28+12-23=?

A piece of rectangular sheet iron is 72 cm long and 60 cm wide. Cut it into a square of the same shape, without any remaining parts. What is the maximum area of each square

Should be able to cut 6 * 6, first cut 60 * 60, cut 10 6 * 6 in 60 * 60, the remaining 12 * 60 cut 6 * 6

The period of a simple harmonic motion of a spring oscillator is t. the moment when the oscillator passes through the equilibrium position is recorded as 0, and the next moment when the kinetic energy of the first system equals three times the potential energy is 0______ ?

It's better to use t as the periodic sign
When t = 0, the moving direction of the oscillator is taken as the positive direction. The mass of the oscillator is set as m and the recovery coefficient is K
The equation of simple harmonic motion of spring oscillator is x = a * sin (2 π T / T)
Velocity v = a * (2 π / T) * cos (2 π T / T)
Period T = 2 π * radical (M / k)
The potential energy is EP = k * x ^ 2 / 2, and the kinetic energy is EK = MV ^ 2 / 2
When the kinetic energy of the first system is equal to three times the potential energy, there is
m*[ A*(2π / T )*cos(2π t / T )]^2 / 2＝3*K*[ A*sin(2π t / T )]^2 / 2
The results show that Tan (2 π T / T) = (radical 3) / 3
SO 2 π T / T = π / 6
The calculated time (the first time when the kinetic energy of the system equals three times the potential energy) is t = t / 12

The length of a rectangle is 80 cm. After cutting off the largest square, a small rectangle is left. The perimeter of this small square is () cm

160cm
Let the width be X. after cutting the largest square, the perimeter of the small rectangle is (80-x + x) × 2
Just draw a picture

Why is pulse the same as heartbeat

The contraction and relaxation of the heart are connected with the blood vessels in the human body, just like a series circuit