There are 10 red, yellow and blue balls in your pocket. Close your eyes and make sure you can touch many four balls of the same color at a time. How many can you touch What's the formula

According to the worst case, if each ball is of different colors, if you touch 3 balls of each type and then touch another one at will, there will always be 4 balls of one color. At most, 3 * 3 + 1 = 10 balls

Put 10 red, yellow, blue, white and green balls in a box, at least how many balls can be taken out to ensure that 4 balls of the same color can be taken out

At least consider the worst case
If you take another ball, there will be four of the same color, so at least take out 3 + 3 + 3 + 3 + 1 = 16 balls

There are two red, yellow and blue balls in three boxes, two in each box. Find the distribution column of the number of boxes with the same color balls

The total number c6,2 multiplied by C4,2 equals 90
0----6*4*2/90=8/15
1----3*3*2*2/90=2/5
2----0
3----6/90=1/15

Red, yellow, blue three colors of the ball each 10 into a box. At least take how many balls, can guarantee two channels
There are 10 balls in red, yellow and blue in each box. At least how many balls can guarantee two balls with the same color? At least how many balls can guarantee two balls with different colors in the channel

1. Get at least two balls, you can get 2 balls:)
2. At least 11 balls must be taken to ensure that there are two balls of different colors. This is the drawer principle

Look at the following column, 1 / 2, 1 / 6, 1 / 12, 1 / 20, 1 / 30 According to the law, the number one is 2011
A. 1 / 2010 b.1/2011 c.1/2010 by 2011 d.1/2011 by 2012

The nth formula is 1 / (n (n + 1))
So choose 1 / 2011 by 2012

Look at the following column: 1 / 2, - 1 / 6, 1 / 12,
Please find out the rule of arrangement and fill in the blanks according to this rule: the eighth number is (), the thirteenth number is ()
----------------------------------------First come, first served-----------------------------------------------
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And why

The general formula is: (- 1) ^ (n 1) / N (n 1), so the eighth and thirteenth terms are - 1 / 72; 1 / 182, respectively

Look at the following column, 1 / 2, - 1 / 6,1 / 12, - 1 / 20
Find the rules and fill in the blanks
What is the ninth number? What is the fourteenth number?
If n is an integer greater than 1, write the nth number according to the above rule

The ninth number is: 1 / (9 * 10) = 1 / 90
The 14th number is: - 1 / (14 * 15) = - 1 / 210
Number n:
If n is odd: 1 / (n * (n + 1))
If n is even: - 1 / (n * (n + 1))

Divide 12 apples into 4 parts, the unit "1" here is (), each part is () of these apples, each part has () apples
Completion

Divide 12 apples into 4 parts, the unit "1" here is (12 apples), each is (1 / 4) of these apples, each has 3 apples

Divide the three apples into four parts, each part is () and each part is ()

Divide the three apples into four parts, each part is (3 / 4), each part is (1 / 4) of three apples

Divide the 12 apples into 4 parts, each of which is divided into a positive number of apples, and the number of apples in each part is different. Excuse me: how many methods are there? How to divide them?

1+2+3+6=12
1+2+4+5=12

There are 10 red, yellow and blue balls in your pocket. Close your eyes and make sure you can touch many four balls of the same color at a time. How many can you touch What's the formula