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0,3,8,15,24,.____ What is the number 2004
Go back and see if there's that "5"
Square of 0 = 1-1
3 = 2 squared-1
8 = the square of 3-1
……
The fourth one is
4016015 = Square-1 of 2004
Observe the law of the following column and fill in the blanks: 0, 1, 3, 6, 10 Then its number 2010 is () and its number n is ()
an=0+1+2+3+...+n-1
a2010=0+1+2+3+...2009
=2010*(0+2009)/2
=29145
an= n(n-1)/2
A mathematical problem, combined total calculation
There are eight groups of numbers a, B, C, D, e, F and G,
The number of numbers in each group is: 8, 6, 6, 3, 5, 4, 48
Now we need to take one number from each of the three groups of numbers (only one number can be taken from the same group). How many methods are there?
It's better to give a formula,
Wrong. Seven numbers,
The number of numbers in each group is not the same, so there should be no skill
The first and second groups and 8 * 6 * (6 + 3 + 5 + 4 + 48) = 3168
Similarly, 6 * 6 * (3 + 5 + 4 + 48) = 2160
6*3*（5+4+48）=1026
3*5*（4+48）=780
5*4*48=960
So there are 3168 + 2160 + 1026 + 780 + 960 = 8094
Row number
Four digits
How many four digits can there be only 3 or 5 or 3 and 5 together?
For example: 3333 3533 3353 3335
Please write down all the numbers for me
Each of the four digits has two choices
A total of 2 * 2 * 2 * 2 = 16
three thousand three hundred and thirty-three
three thousand three hundred and thirty-five
three thousand three hundred and fifty-three
three thousand five hundred and thirty-three
five thousand three hundred and thirty-three
three thousand three hundred and fifty-five
three thousand five hundred and fifty-three
five thousand five hundred and thirty-three
three thousand five hundred and thirty-five
five thousand three hundred and fifty-three
five thousand three hundred and thirty-five
three thousand five hundred and fifty-five
five thousand three hundred and fifty-five
five thousand five hundred and thirty-five
five thousand five hundred and fifty-three
five thousand five hundred and fifty-five
Mathematical problems on permutation
3 boys and 2 girls. 1. How many kinds of arrangements do boys have to stand at both ends
2. How many kinds of three boys must be arranged together? 3. How many kinds of arrangement are there in the order of a, B and C?
1. There are 5 people in total, because boy a has to stand at both ends, which means there are only 4 people in the row, so there are 4 * 3 * 2 * 1 = 24
2. Three boys have 3 * 2 * 1 species. If we regard it as a whole, there are 3 * 2 * 1 species
So 3 * 2 * 1 * 3 * 2 * 1 = 36 species
3. The same 1, because the position of 3 people has been determined, so only 2 people are arranged, there are 2 * 1 = 2 kinds
It takes 3 hours for a ship to go downstream for 36 km and upstream for 24 km. The water velocity and the ship's velocity in still water are calculated
The current speed is 2 km / h, and the ship's speed in still water is 10 km / h
36 / 3 = 12 (km / h)
24 / 3 = 8 (km / h)
(12-8) / 2 = 2 (km / h) (water velocity)
12-2 = 10 (km / h) (speed of ship in still water)
8 7 6 5 4 3 2 1 = 36 math problem Oh, friends help
+ -×÷
Can be used, can also be bracketed
At least five results are required
8+7+6+5+4+3+2+1=36,
(8*7-6-5-4-3-2)*1=36
8-7+5*6+4+3-2*1=36
8+7-6+5*4+3*2+1=36
8+7+6+5+4*3-2*1=36
8+7+6+5+4*3*1-2=36
8+7+6+5+4+3*2*1=36
It takes 3 hours for a ship to go down 36 km downstream and 3 hours for a ship to go up 24 km upstream
It takes 3 hours for a ship to go down 36 km downstream and 3 hours for a ship to go up 24 km upstream
Please write down the process: ship speed + water speed = 36 / 3 = 12 ship speed - water speed = 24 / 3 = 8 ship speed = 10 speed in still water: (36 △ 3 + 24 △ 3) △ 2 = 10 (km / h) water flow
There are five numbers in total, and the sum of every four numbers is 15, 22, 23, 24 and 32 respectively
Sum of 5 numbers: (15 + 22 + 23 + 24 + 32) / 4 = 29
So the five numbers are: 29-15 = 14
29-22=7
29-23=6
29-24=5
29-32=-3
There are four numbers, and the sum of every three numbers is 15, 22, 23 and 24 respectively
Let the sum of the four numbers be X. according to the meaning of the question, we get: (X-15) + (x-22) + (x-23) + (x-24) = x, and the solution is: x = 28, then the four numbers are: 28-15 = 13, 28-22 = 6, 28-23 = 5, 28-24 = 4; answer: the four numbers are 4, 5, 6, 13
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