Probability 2 questions, trouble to give an explanation.

1. According to the title, there are 5 situations in which a pair of socks is taken out.

There are a total of 45 ways to take 2 socks (10x9 2), so the probability of taking out a pair is 1 9 (5 45)2, assuming that the 2 socks taken out are exactly one pair, and then take 2 from the remaining 10, there are a total of 45 ways to take (10x9 2).

In order to avoid the remaining 2 also exactly one pair, use 45-5=40 species.

There are 6 different pairs of socks, so 40x6 has a total of 240 cases.

There are only 495 cases when I take four out of 12 socks.

The probability of exactly a pair being paired is 240 495=16 33

Take any 4 of the 6 pairs of gloves, i.e. 12 gloves, a total of 4 ways to take c(12) (the base number in parentheses).

Take any one of the 6 pairs, c(6)1, and choose 2 pairs from the remaining 5 pairs c(5)2 choose 1 of the 2 pairs.

i.e. c(2)1 c(2)1

Total probability c(6)1 c(5)2 c(2)1 c(2)1 divided by c(12)4=16 33

1.The numerator is (c2,2)*5=5 and the denominator is (. So the answer is 1 9.

2.The numerator is ( The denominator is (. So the answer is 16 33.

The probability that the policyholder will obey the normal distribution requirement of n(280,800 2) is.

p(x≤2700 000/10000}

Construct Statistics|x-280|/800

Then check the standard normal distribution table.

Take the logarithm of l and then find the derivative of p, and find the extreme condition of log(l).

Simple calculations, conversion of variance expressions to in-question expressions. If you want to save time, you can also make n=2, and you can directly determine the answer.

Analysis: 1) Remember that "A draws to the multiple-choice question, B draws to the true/false question" as event a, A draws the multiple-choice question has 6 kinds of drawing, and B draws the true/false question has 4 kinds of drawing, so the basic number of events of event A is 6 4 = 24

p(a)=m/(10*9)=4/15.

2) Consider the opposite side of the problem first: "At least one of A and B has drawn a multiple-choice question" The opposing event is "Neither A nor B has drawn a multiple-choice question", that is, both have drawn a true/false question.

Remember that "both A and B draw true/false questions" is event B, and "at least one person draws multiple choice questions" is event C, then B contains the number of basic events is 4 3 = 12

p(b)=12 (10*9)=2 15 is obtained from the classical generalized probability formula, which is obtained from the nature of the opposing event.

p(c)=1-p(b)=

Analyze the situation of not being late, calculate the probability.

a No red light, probability:

b Encounter 1 red light, probability: c(5,1)*

c encounters 2 red lights, probability: c(5,2)*

Probability of punctual attendance:

For Xiao Zheng, there are two possibilities, sick and healthy.

Assuming that Xiao Zheng is sick, the probability: 1%.

Excluding the influencing factors of environmental and physical differences, the probability of prevalence: 1%* (assuming that Xiao Zheng is healthy, the probability: 99%.

Excluding environmental and other diseases, the probability of disease: (1-1%)* then the probability of Xiao Zheng's disease:

There are four colors, 13 sheets each.

The first one: any.

The second of this stupid color: 12 51 (the number of cards of the same color divided by the number of remaining cards) and the third of the same color: 11 50

The probability of the line with the forest = (12*11) (51*50) is about 1 20

a=5 25 20 percent.

b = 5 25 = 20 percent.

Since it's a multiple-choice question, you just need to know that C is correct.

Distribution function, monotonic, from 0 to 1

a.Obviously there is a problem, the integral is 2, and it can't be the probability density bThis does not guarantee that the integral will be 1, and in a random example, the product of two identical [0,2] evenly distributed is not.

d.Similar to a, when the function tends to infinity, it tends to 2, which does not conform to the property of probability distribution functions.