The solution of classical probability problem, Four different language books and two different mathematics books. What's the probability of taking out any two of them,

The solution of classical probability problem, Four different language books and two different mathematics books. What's the probability of taking out any two of them,

The opposite event of "taking out mathematics books" is "all the books taken out are Chinese books"
So p = 1-C (4,2) / C (6,2) = 1-6 / 15 = 3 / 5

How does the permutation and combination formula CNM (n is subscript, M is superscript) = n! / m! (n-m)! Come from

Forget the permutation formula of high school, remember CNM = n! / m! (n-m)! Forget the formula of anm,
Tell me the formula of anm. If you have a free website to learn advanced mathematics, I will add another 50 points
A22 = 2, so it's definitely not Ann = n! / m! It's like Ann = n! / (n-m)! But I'm not sure

http://wenku.baidu.com/view/63a7a450ad02de80d4d840e8.html

Classified conductive non electrolyte electrolyte can not conduct electricity
① NaOH solution (2) copper wire (3) liquid HCl (4) hydrochloric acid (5) dilute sulfuric acid (6) liquid ammonia (7) ammonia water (8) SO2 (9) cholangiocarpus crystal (10) molten NaCl (11) sucrose crystal (12) alcohol (9) alcohol solution
What can conduct electricity in the above state is
It's a non electrolyte
The electrolyte in the above state cannot conduct electricity
=Please explain again

According to the definition of the first question, the compound that can conduct electricity in aqueous solution or molten state is electrolyte

"I did a time experiment! It really verified Einstein's hypothesis of special relativity!" can you send me that video

…… Depressed It took a hundred years for a paper to be realized Well, do you have a satellite

What is the reason of conducting electricity in electrolyte solution or molten electrolyte? What is the essence of conducting electricity?

The directional movement of ions in a solution (or liquid)
It's an electrolytic reaction

Einstein's special theory of relativity proves that the specific characteristics of time and space change with the speed of the object?
A. Absolute B. relative C. infinite D. finite
Please elaborate on the reasons···

B. Time and space are relative, which is the basic principle of special relativity

No repetition of 1000 oral arithmetic questions with answers

1.45+15×6= 135
2.250÷5×8=400
3.6×5÷2×4=60
4.30×3+8=98
5.400÷4+20×5= 200
6.10+12÷3+20=34
7.(80÷20+80)÷4=21
8.70+(100-10×5)=120
9.360÷40= 9
10.40×20= 800
11.80-25= 55
12.70+45=115
13.90×2= 180
14.16×6= 96
15.300×6= 1800
16.540÷9=60
17.30×20= 600
18.400÷4= 100
19.350-80= 270
20.160+70=230
21.18-64÷8= 10
22.42÷6+20=27
23.40-5×7= 5
24.80+60÷3=100
25.41+18÷2= 50
26.75-11×5= 20
27.42+7-29= 20
28.5600÷80=70
29.25×16= 400
30.120×25= 3000
31.36×11= 396
32.1025÷25=41
33.336+70= 406
34.25×9×4= 900
35.200-33×3= 101
36.3020-1010=2010
37.12×50= 600
38.25×8= 200
39.23×11= 253
40.125÷25=5
41.4200-2200=2000
42.220+80= 300
43.20×8×5= 800
44.600-3×200=0
45.20+20÷2= 30
46.35-25÷5= 30
47.36+8-40= 4
48.2800÷40=70
49.98÷14 = 7
50.96÷24 = 4
51.56÷14 =4
52.65÷13 = 5
53.75÷15 = 5
54.120÷24 =5
55.200÷25 = 8
56.800÷16 = 50
57.840÷21 =40
58.560÷14 = 40
59.390÷13 = 30
60.600÷15 =40
61.72÷24 = 3
62.85÷17 = 5
63.90÷15 =6
64.96÷16 = 6
65.78÷26 = 4
66.51÷17 =3
67.80÷40 = 2
68.100÷20 = 5
69.100÷4 =25
70.240÷40 = 6
71.920÷4 = 230
72.300÷60=5
73.64÷2 = 32
74.64÷4 = 16
75.50÷5 =10
76.60÷8 = 7.5
77.96÷4 = 24
78.90÷6 =15
79.400+80 = 480
80.400-80 = 320
81.40×80 =3200
82.400÷80 = 5
83.48÷16 = 3
84.96÷24 =4
85.160×5= 800
86.4×250= 1000
87.0×518= 0
88.10×76= 760
89.36×10=360
90.15×6= 90
91.24×3= 72
92.5×18= 90
93.26×4= 74
94.7×15=105
95.32×30= 960
96.40×15= 600
97.60×12= 720
98.23×30= 690
99.30×50=1500
100.5×700=3500123+25=148 123-35=88 56×7=392 135÷5=27
248+89=337 146-23=123 155×5=775 456-12=38
456+45=501 546-457=89 45×10=451 564-12=47
879+54=933 896-546=350 56×12=672 45-5=9
457+456=913
7+14=21 18-9=9
8+16=24 25-5=20
9+18=27 56-45=11
10+20=30 45-23=22
11+22=33 78-23=55
12+24=36
10-3=7
15-4=11
20-5=15
25-6=19
30-7=23
35-8=27
40-9=31
45-10=35
50-11=39
55-12=43
60-13=47
65-14=51
70-15=55
75-16=59
80-17=63
85-18=67
90-19=71
95-20=75
100-21=79
105-22=83
110-23=87
115-24=91
120-25=95
125-26=99
130-27=103
13+26=39
14+28=42
15+30=45
16+32=48
18+36=54
19+38=57
20+40=60
21+42=63
22+44=66
23+46=69
24+48=72
25+50=75
26+52=78
27+54=81
28+56=84
29+58=87
30+60=90
31+62=93
32+64=96
33+66=99
5 ÷1=5
10 ÷2=5
15 ÷3=5
20 ÷4=5
25 ÷5=5
30 ÷6=5
35 ÷7=5
40 ÷8=5
45 ÷9=5
50 ÷10=5
55 ÷11=5
65 ÷13=5
70 ÷14=5
75 ÷15=5
80 ÷16=5
85 ÷17=5
90 ÷18=5
95 ÷19=5
100 ÷20=5

What is the speed time image

Speed, of course. Speed

I am in urgent need of 1000 oral arithmetic questions! It's better to divide them into 10 times and 100 at a time!

32＋9＝ 60×3＝ 50÷2＝ 22×4＝ 66÷6＝ 71－7＝ 400÷2＝ 90÷3＝ 69÷3＝ 62÷2＝ 28＋17＝ 30×8＝ 800÷4＝ 13×2＝ 20×4＝ 64－36＝ 31×2＝ 36÷3＝ 84÷4＝ 140÷7＝ 15×4＝ 9×80＝ 15×40＝ 49×10＝ 1...