Primary School Olympiad, writing process, thank you!

After mixing, pour out half of the solution, in fact, the amount of alcohol and water in the poured solution is the same as the rest of the solution.

For example, if a 200-gram solution contains 30 grams of alcohol, then after dividing it into halves and halves, each part contains 15 grams of alcohol.

In this way, just focus on the amount of alcohol in the two containers.

At the beginning, 800 grams in A and 0 grams in B.

For the first time, A pours 400 grams of alcohol to B first, and the remaining 400 grams are left, and B has a total of 640 + 400 = 1040 grams of solution, containing 400 grams of alcohol; Then B poured back to A for a total of 1040 2 = 520 grams, containing 400 2 = 200 grams of alcohol. A has a total of 400 + 520 = 920 grams, and contains 400 + 200 = 600 grams of alcohol.

That is, the first finish, A and B's (alcohol content, total weight) is.

A (600, 920), B (200, 520).

The second time, A pours out to B is equivalent to (600 2,920 2), which is (300, 460).

B becomes (200+300, 520+460) = (500, 980).

Then B pours to A(500 2, 980 2) = (250, 490).

A becomes (300+250, 460+490) = (550, 950).

At this time, A and B are (550, 950), 250, 490).

Thirdly, A->B: (550 2, 950 2) = (275, 475).

B: (250+275, 490+475) = (525, 965).

B->A: (525 2, 965 2) = (, A: (275+, 475+ = (, so at the end there are grams of solution in container A, which contains grams of alcohol.

Weight of solution in a:

The total weight of A and B remains unchanged, which is 800 + 640 = 1440 grams.

After the first time: 800 2 + (1440-800 2) 2 = 920 grams.

After the second time: 920 2 + (1440-920 2) 2 = 950 grams.

After the third time: 950 2 + (1440-950 2) 2 = grams.

Pure alcohol in the first place:

Pour half at a time, and pour back half of half at a time.

After each operation, the remaining original: 1-1 2+1 2*1 2=3 4 After three operations, the pure alcohol is: 800 3 4 3 4 3 4 = grams.

List: A Alcohol, A Water, B Alcohol, B Water.

Starting 800 0 0 640

First operation 400 0 400 640

Second operation 300 160 500 480 Third operation 275 200 525 440 After third operation: A pure alcohol, A solution.

It is set in x minutes and the distance is y meters.

y=80*(x+5)

y=80*10+200*（x-10-1)

x=15y=1600

1.There are eight numbers a, b, c, d, e, f, g, and h in a series of equal differences, and the average of the two numbers d and e is known to be 9, then the average of the eight numbers a, b, c, d, e, f, g, and h is 9 and 72

2.In a foreign language test, the average score of Zhao, Qian, Sun, Li, and Friday was 4 points less than the average score of Sun, Li, and Zhouren, and the average score of Zhao and Qian was 75 points. 81

3.If the sum of the middle two numbers d and e is 16, the average of the eight numbers is 8 and the sum of these eight numbers is 64

Four numbers, remove one number at a time, and average the remaining three numbers, so that the calculation is done four times, and the following four numbers are obtainedQ: What is the average of the four numbers A, B, C, and D.

5.There are four numbers, three of them are selected at a time, their average is calculated, and another number is added, and the other number is calculated 4 times in this way, and each is obtained. Then the original four numbers, the largest number is 33

Elementary school ah=mouth=

Question 1 9,72

Question 2 81

Question 3 8,64

Question 4 28

Question 5 32

The process doesn't ask me.

Suppose that if there is x households with one child, then there are (5000-x) 2 families with two children, and (5000-x) 2 families with zero children. (As mentioned in the title, there are no more than two per household, i.e.: one, two, zero).

Then there are a total of x+2*[(5000-x) 2]+0*(5000-x) 2=5000 in the town.

There are 5,000 children.

There are 5,000 children in the town.

From "half of the remaining families have two children per household", it can be seen that the other half of the remaining families have no children per household, that is, the remaining families have only one child per household on average, plus the previous sentence "some families have one child per household".

This is an estimation problem, calculate the maximum and minimum values, between 10000 and 5000, or less than 10000, more than 5000

Addendum: There are 5,000 children in this town; From "half of the remaining families have two children per household", it can be seen that the other half of the remaining families have no children per household, that is, the remaining families have only one child per household on average, plus the previous sentence "some families have one child per household".

If the date of going home is also in September, then the five-day date is consecutive, so the middle day, which is the third day, is the average of the sum of the five days, that is, 90 5 = the 16th of the month is obviously contradictory to the end of September, so Mr. Wang only went home in early October.

Because 28 + 29 + 30 + 1 + 2 = 90, Mr. Wang went home on October 2.

Answer:

Long Answer:This number is written, and keeping one decimal place is 9(Be sure not to drop zero, otherwise it will become a reserved integer), accurate to the percentile.

Analysis:

8 one gives 8

9 tenths are derived.

5 hundredths to get it.

2 derived.

Summing.

Keep one decimal place2greater than 5, rounded, further one, for.

Accurate to the percentile is the same as keeping two decimal places2 is less than 4, rounded, rounded, for.

A number consists of 8 one, 9 tenths, 5 hundredths and 2, this number is written as ( ) to keep one decimal place is ( ) accurate to the percentile is ( ).

8 1's equals 8

9 1/10 equals 9/10, that is.

Five hundredths equals five percent.

2 is. It all adds up.

Keep one decimal place approximately equal to and rounded.

Accurate to the percentile, i.e. keeping two decimal places approximately equal to.

Writing (keep one decimal place (exact percentile) (.)

Hello, I hope mine is helpful to you.

Keeping one decimal place is.

Accurate to the percentile.