Permutations, combinations, groupings, and problems are always not, and they are teachable

I don't know if the balls are the same.

You can get some stimulants.

<> "The formula for calculating permutations and combinations is: a(n,m) = n! /n-m)!

Its loss in the mountains n!denotes the factorial of n, i.e., n! =n * n-1) *n-2) .

1。For A32, the table selects 3 elements from 32 different elements to arrange the number. The calculation is as follows:

a(32,3) =32! /32-3)! 32!

29!= 32 * 31 * 30 = 29,920, so digging A32 is equal to 29,920.

I lost my top2, poor thing! Bi Ran Pie.

Solution: 1: If there is no 0 in the 4 numbers, then directly select 4 numbers from 1, 2, 3, 4, 5, and then arrange them all.

is a(5)4=120.

2: If there is 0, then you should choose 3 more numbers from 1, 2, 3, 4, 5, it is c(5)3=10, because 0 cannot be ranked in the thousands, so you should choose 1 of the 3 numbers from the selection of regret in the thousand position is c (paragraph cover 3) 1 = 3

Then the remaining 3 numbers are arranged in full a(3)3=6;

So it's 10 3 6 = 180.

This makes up: 120 + 180 = 300 different four-digit numbers.

c (The first class selects 3 from the nine numbers, how these three numbers become dusty are able to form a triple alliance of brothers, so it is a potato cover combination, and the three numbers are all arranged, so it is an arrangement.)

The second category is to take 3 of the remaining six types, and the same goes for the following.

(1) There is a return: the probability of getting the white ball each time is 8 13;The probability of getting a red ball each time is 5 13. The question requires four balls, two white and two red, regardless of which time the white ball is taken, which time the red ball is taken, a total of C42 = 6 ways to take it.

p=6*（8/13）*（8/13）*（5/13）*（5/13）；

2) No return: The method is the same as above, and there are also six kinds. This probability is difficult to calculate, so we must list all 6 situations and calculate them one by one.

3) There are also six types of one-time ball pick-ups. P=c82*c52 c134 halo! At first, I thought you had to calculate the probability of each method, but after answering half of the answer, I saw your question, and I simply wrote it out for you.

1) The question is the number of kinds of extraction, not probability, so only consider the order of taking out 2 white balls in 4 balls, c42 2=4*3 2=6

2 and 3 are the same, both are 6 types.

c31*c42*c41=72

2 rows, there are 3 horizontal lines, select one C31

There are 4 vertices on each horizontal line, take 2, c42

There are 4 more points in the vertical direction of the 2 points taken on the horizontal line. Take any point of c41 or c41*c32*c61 (from 3 to hand, the answer is the same).