There are two layers of books on the bookshelf. The first layer has 50 more books than the whole 3 / 5. The second layer is the whole 1 / 3. How many books are there on the bookshelf?

50 books account for 3 / 5 + 1 / 3-1 = 1 / 15 of the whole bookshelf
50 / (3 / 5 + 1 / 3-1) = 750 copies

There are two layers of books on the shelf. The first layer is 50 more than three fifths of all books, and the second layer is one third of all books. How many books are there on the shelf

There are two layers of books on the bookshelf. The first layer has 90 more than all 35 books, and the second layer has all 13. How many books are there on the bookshelf?

A: there are 1350 books on the shelf

There are two layers of books on the bookshelf. The first layer has 90 more than all 35 books, and the second layer has all 13. How many books are there on the bookshelf?

A: there are 1350 books on the shelf

Factorization
x^6-2x^4+6x^3+x^2-6x+9

Solution: original formula = x ^ 6-2x ^ 3 (x-3) + (x ^ 2-6x + 9)
=x^6-2x^3(x-3)+(x-3)^2
=(x^3-(x-3))^2
=(x^3-x+3)^2
=(x^3-x+3)(x^3-x+3)

How many hours can a 3-watt thing last?
Using equation

Let's set up three kilowatt hours for 50 Watt things,
（50/1000）×x=3
0.05x=3
X = 60 hours
A: three kilowatt hours for a 50 Watt thing

High school mathematics compulsory five equal ratio series
The sum of the first n terms of the sequence {an} is SN. It is known that A1 = 1, a (n + 1) = Sn (n + 2) / n
(n=1,2,3...)
It is proved that the sequence {Sn / N} is an equal ratio sequence

It is converted to the recurrence of Sn
A(n+1)=Sn(n+2)/n-----------S(n+1）-Sn=Sn(n+2)/n
transposition
S(n+1)=Sn(n+2)/n +Sn
S(n+1)=Sn(2n+2)/n=2*Sn(n+1)/n
Divide (n + 1) and you get it
S(n+1)/(n+1)=2* Sn/n
So the sequence {Sn / N} is an equal ratio sequence

Two "220 V 40 W" electric lamps are connected in series and then connected to the 220 V lighting circuit. What is the sum of the actual power of the two electric lamps?

First calculate the resistance value of load r = u * U / P = 220 * 220 / 40 = 1210 Ω, the total load of two series connection is 1210 * 2 = 2420 Ω, then calculate the power P = u * U / r = 220 * 220 / 2420 = 20W
In fact, it can be concluded that the actual power of two bulbs with the same power in series is half of that of a single bulb

Simple operation of 1,2 / 5,3 / 25,4 / 75
Write the fifth number

1/25

When a DC motor has a rated voltage of 220 V and a coil resistance of 1.0 ohm and a current of 5.0 a under normal operation, what is the heat and mechanical energy generated in one hour

When u = 220 V, I = 5 A, t = 1 h = 3 600 s, w total = uit = 220 V * 5 A * 3 600 s = 39 60000 J, when I = 5 A, r = 1 Ω, t = 1 h = 3 600 s, Q heat = I & # 178; RT = (5 a) & # 178; * 1 Ω * 3 600 s = 90000 JW, mechanical = w total - Q heat = 39 60000 j-90000 J = 38 70000 J. A: the generated heat is 90000 J, the mechanical energy is 3870000 J

There are two layers of books on the bookshelf. The first layer has 50 more books than the whole 3 / 5. The second layer is the whole 1 / 3. How many books are there on the bookshelf?