There are two children in a family, one of whom is known to be a girl, and the probability that the other child is also a girl is? (the probability that each child is a boy is equal to that of a girl) Our teacher talked about four basic events: male, male, female, male and female. Then there are three other events except "male", so it is 1 / 3 But I think men and women, as well as women and men, belong to the same basic event. It should be one half,

There are two children in a family, one of whom is known to be a girl, and the probability that the other child is also a girl is? (the probability that each child is a boy is equal to that of a girl) Our teacher talked about four basic events: male, male, female, male and female. Then there are three other events except "male", so it is 1 / 3 But I think men and women, as well as women and men, belong to the same basic event. It should be one half,

Of the two children, one is a girl. This is called conditional probability, which is the probability of B under a, so it's not 1 / 2. The other is the probability of a girl, which is 1 / 3 as the teacher said

A family has three children, (1) the probability of having two boys and one girl in the family, (2) the probability of having at least one boy in the family

Use B and G to represent boys and girls respectively, and use "tree" to list all the results: the probability of the family having two boys and one girl is 38, and the probability of the family having at least one boy is 78

Suppose that the probability of success in one trial is p, and 100 independent repeated trials are carried out, then the maximum variance of success times ξ is 0______ ．

From the variance formula of the independent repeated test, we can get D ξ = NPQ ≤ n (P + Q2) 2 = N4, the equal sign holds when p = q = 12, and the answer is: 25

Elements are created by____ Or____ A general term for a class of atoms

Elements are created by__ Proton number__ Or__ Nuclear charge number__ A general term for a class of atoms

The formula of arithmetic sequence

1+2+…… +n=n(n-1)/2

What does the type of element depend on?
1. What are the outermost electron number 2, neutron number 3, relative atomic mass 4, proton number and why?

The number of protons determines the type of elements, because the number of protons in different elements must be different. There are many kinds of electrons with the same number in the outermost layer, and there are many kinds of neutrons with the same number. Although the relative atomic mass is not equal, it is calculated by the artificial rules!

The reasoning of the formula for finding the final term of the second order arithmetic sequence

If you say "second order arithmetic sequence" means such a sequence {a (n)}: a (n) - A (n-1) is arithmetic sequence, then its general term formula a (n) = (n-1) a (2) - (n-2) a (1) + (n-1) (n-2) d / 2, the derivation idea is: B (n) = a (n) - A (n-1), then B (n) - B (n-1) = D; thus a (n) = 2A (n-1) - A (n-2)

What determines the kind of atom is ()?

Proton number

What is the formula for finding the final term of arithmetic sequence?

It's the general term formula
For example, 1,3.5
Find the nth term, an = 1 + (n-1) 2 = 2N-1

It is in the atomic structure that determines the kind of elements
A proton number
B neutron number
C electron number
D relative atomic mass

A