Calculation (1 + 19 ＼ 39 × 1) + (1 + 19 ＼ 39 × 2) + (1 + 19 ＼ 39 × 3) + +(1 + 19 ＼ 39 × 12) is calculated by a simple method,

Original formula = 12 * 1 + 19 / 39 * (1 + 2 +...) +12）=12=19/39*12(12+1)/2=50

Will the electric motor 500W good or 800W good

It depends on your use. If it's only for personal use, 500W is enough. If you often load goods, 800W is used

Two and five out of seven minus thirteen out of fourteen plus two out of seven

=2 and 5 / 7 plus 2 / 7 minus 13 / 14
=3-13/14
=2 and 1 / 14

A classmate noticed that the light bulb in his home was brighter than usual. He guessed that the voltage might not be equal to 220 v. in order to confirm his conjecture, he did the following experiment: turn off other electrical appliances in his home, turn on only a "220 V 100 W" electric light, observe the watt hour meter marked "3000 revs / kW · H", and find that the meter turns 121 turns in 20 minutes__ W. What is the actual voltage at this time_ V
Ask the key of electric power problem, as long as I can't get this kind of problem, how can I do it?

The actual voltage is u, the actual power is p, and the resistance is r
The watt hour meter is 3000 rpm. That is to say, 3000 rpm an hour, and the work done is 1 kwh
So the actual power P = [(121 / 3000) * 1] / (20 / 60) = 0.121kw = 121w
From P = u * U / R, u * U / u (amount) * u (amount) = P / P (amount)
Substituting the data, we can see that u = 242v

Can 38.5-15.38 + 61.25-4.6 be easily calculated?
Sorry, wrong number. Yes
38.5-15.38+61.25-4.62
Can it be easily calculated?

38.5-15.38+61.25-4.62
=（38.5+61.25）-（15.38+4.62）
=99.75-20
=77.75;
If you don't understand this question, you can ask,

If the total half bias method is used to measure the internal resistance of an ammeter with a range of 100ua is 600ohm, it is necessary to refit the ammeter into a voltmeter with a range of 5V
If the internal resistance of a 100 UA ammeter is 600 Ω measured by the total half bias method, the method to refit the ammeter into a 5 V voltmeter is to connect the ammeter () with a resistance of () Ω

When the ammeter is refitted into a voltage meter with a range of 5V, the refitting method is to connect a resistance of (4.94 * 10 ^ 4) ohm with the ammeter (in series)
100uA=10^(-4)A
R total = 5 / 10 ^ (- 4) = 5 * 10 ^ 4 Ω
R string = 5 * 10 ^ 4-600 = 4.94 * 10 ^ 4 Ω

Need 50 real mixed operation questions. It's better to attach the answer

1.3/7 × 49/9 - 4/3
2.8/9 × 15/36 + 1/27
3.12× 5/6 – 2/9 ×3
4.8× 5/4 + 1/4
5.6÷ 3/8 – 3/8 ÷6
6.4/7 × 5/9 + 3/7 × 5/9
7.5/2 -（ 3/2 + 4/5 ）
8.7/8 + （ 1/8 + 1/9 ）
9.9 × 5/6 + 5/6
10.3/4 × 8/9 - 1/3
11.7 × 5/49 + 3/14
12.6 ×（ 1/2 + 2/3 ）
13.8 × 4/5 + 8 × 11/5
14.31 × 5/6 – 5/6
15.9/7 - （ 2/7 – 10/21 ）
16.5/9 × 18 – 14 × 2/7
17.4/5 × 25/16 + 2/3 × 3/4
18.14 × 8/7 – 5/6 × 12/15
19.17/32 – 3/4 × 9/24
20.3 × 2/9 + 1/3
21.5/7 × 3/25 + 3/7
22.3/14 ×× 2/3 + 1/6
23.1/5 × 2/3 + 5/6
24.9/22 + 1/11 ÷ 1/2
25.5/3 × 11/5 + 4/3
26.45 × 2/3 + 1/3 × 15
27.7/19 + 12/19 × 5/6
28.1/4 + 3/4 ÷ 2/3
29.8/7 × 21/16 + 1/2
30.101 × 1/5 – 1/5 × 21
31.50＋160÷40 （58+370）÷（64-45）
32.120-144÷18+35
33.347+45×2-4160÷52
34 （58+37）÷（64-9×5）
35.95÷（64-45）
36.178-145÷5×6+42 420+580-64×21÷28
37.812-700÷（9+31×11）
38.85+14×（14+208÷26）
39.（284+16）×（512-8208÷18）
40.120-36×4÷18+35
41.（58+37）÷（64-9×5）
42.( 6.8-6.8×0.55)÷8.5
43.0.12× 4.8÷0.12×4.8
44.（3.2×1.5+2.5）÷1.6
45.6-1.6÷4= 5.38+7.85-5.37
46.7.2÷0.8-1.2×5
47.6.5×（4.8-1.2×4）
48.1 0.15-10.75×0.4-5.7
49.5.8×（3.87-0.13）+4.2×3.74
50.32.52-（6+9.728÷3.2）×2.5

All kinds of formulas of people's education press in the third grade of Physics

The formula is in the attachment. Download and check it by yourself. It's the word version
Is the total review for students, not just the formula of the third day

600 words of beautiful composition in life

In the life of junior high school, there are happiness, distress, confusion and sadness. Too many emotions are in harmony. The short life of junior high school becomes simple and complex, which makes people worry and aftertaste
On the junior high school, on behalf of their own grown up, in the is not that let people spoil the love of the protection of the "little princess", "little master". On behalf of their own ideas and freedom, is no longer a will only listen to their parents, no independent person. Although there is freedom, but life is out of control; although growing up, but some things can not be completed by one person alone
In the past, what difficulties in school, sometimes teachers can help, naturally relaxed. Learning is not very urgent, even if they can't control themselves, at least there are strict father, mother. At home, they are spoiled and protected, what things they can't take care of, there are parents around them. Life is orderly and orderly
But in junior high school, everything naturally changed. It seems that they have entered a strange world. They solve the small things by themselves in school. The school is also very nervous, and there are too many homework. When they can't control themselves, their parents don't care much either. Because they think that they should learn to be self-conscious when they go to junior high school. At home, now they are not the "little princess" who used to be spoiled and protected. They should pay attention to everything, Because they said that when they grow up, they should have their own opinions. In this way, junior high school life is spent in chaos. Every day's life has no order
In junior high school life, I always shed tears when I encounter troubles and sad things. In front of my classmates, I always smile and pretend to be strong. In fact, smile is just to cover up my sad side. Now I understand the meaning of "tears in smile". Because I don't have my parents' spacious shoulders. When I am in pain, that shoulder is like a warm stove, It's like a wandering child has found a home. But now, I have no home. When I'm sad, I have to cry. I have no shoulder to rely on. Because the person on my shoulder is me
Everyone said that junior high school life is free and easy. Before, I was naturally looking forward to growing up soon and enjoying junior high school life. I didn't know until I got it. The price of freedom is sadness. It's too big and painful. I can't reflect it for a moment
When I was depressed, I always thought about everything in the past. I thought that as long as I got good grades, my parents would love me more. But when I told them everything in school, they only said "work hard". Then I put myself into work, I have been thinking: Maybe my parents just want to use the extension of disdain to let me pay more attention to them with study and attract them. So I am working harder to recover my previous achievements and myself
Junior high school life left countless pain and happiness. Pain is short, happiness is permanent. This is what I always believe
Perhaps in your junior high school life, there have been countless bitter and sweet bar
For the former self, junior high school life is a mysterious gossamer, always want to set off its real face, to see the surprise inside; but now opened, it brings a lot of distress, confusion, happiness, sadness and so on. This surprise really makes me unable to accept in a moment. But it still comes in a rush, If you want to go back, you can't go back. Maybe it will make you remember and savor junior high school life more

What's the difference between power and horsepower of a diesel engine
1 kW = how much horsepower

1 HP = 0.735 kw

Calculation (1 + 19 ＼ 39 × 1) + (1 + 19 ＼ 39 × 2) + (1 + 19 ＼ 39 × 3) + +(1 + 19 ＼ 39 × 12) is calculated by a simple method,