Students, the distance between every eight trees is 21 meters. According to this calculation, what is the distance between planting 20 trees? 2. The park plans to place benches on one side of a 442 meter long path every 20 meters. Each chair is 2 meters long. How many benches should be placed from the beginning to the end?

Students, the distance between every eight trees is 21 meters. According to this calculation, what is the distance between planting 20 trees? 2. The park plans to place benches on one side of a 442 meter long path every 20 meters. Each chair is 2 meters long. How many benches should be placed from the beginning to the end?

Students, the distance between every eight trees is 21 meters. According to this calculation, what is the distance between planting 20 trees?
21 * (20-1) = 399 (m) a: the distance is 399 M
2. The park plans to place benches on one side of a 442 meter long road every 20 meters. Each chair is 2 meters long. How many benches should be placed from the beginning to the end?
(442 + 20) / (20 + 2) = 21 (pieces) a: a total of 21 pieces
Analysis: these two are interval problems
1. If you plant 20 trees, there will be 19 intervals
Because each interval is 21 meters, we can use 21 * 19 = 399 meters
2. This is the reverse of the previous one
You just need to turn your mind to understand

I have three passengers. I have twice as many passengers as you. I have 24 passengers
———?————；————?————；
———?————；————?————.
How do you write it?

How many passengers does the second person have? 3 × 2 = 6 A: the second person has 6 passengers
How many times the number of passengers of the third person is that of the second person? 24 (3 × 2) = 4 A: the number of passengers of the third person is four times that of the second person
How many fewer passengers does the first person have than the second person? 3 × 2-3 = 3 (seats) a: the first person has three fewer passengers than the second person
How many times the number of passengers of the third person is that of the first person

It took Xiao Ming three days to finish reading a story book. On the first day, he read 30% of the whole book. On the second day, he read 50% more than the first day. On the third day, he read 25 pages. How many pages are there in this book? On the second day, 75% of the number of Volleyball in the sports room is equivalent to 80% of the number of basketball. Basketball is 10 less than volleyball. How many volleyball and basketball are there in the sports room?

(1) 25 ÷ [1-30% - 30% × (1 + 50%)] = 100 (pages)
Note: 1 + 50% is the proportion of the second day to the first day,
30% × (1 + 50%) is the proportion of the next day in the whole book
(2) Let 75% of the number of volleyball be X,
X÷75%－X÷80%＝10
X×100／75－X×100/80 ＝10
X× （100／75－100/80）＝10
X×1/12＝10
X＝120
The number of volleyball is 120 ／ 75% = 160 (pieces)
The number of basketball is 120 △ 80% = 150 (pieces)
160 + 150 = 310
A: there are 310

In triangle ABC and triangle a'b'c ', AB / a'B' = BC / b'c '= Ca / c'a' = 5 / 2, and the difference of their perimeter is 60cm, what are the perimeter of triangle ABC and triangle a'b'c '?

AB=5/2 A'B' AB-A'B'=3/2 A'B'
BC=5/2 B'C' BC-B'C'=3/2 B'C'
CA=5/2 C'A' CA-C'A'=3/2 C'A'
60=3/2 (A'B'+B'C'+C'A')
The perimeter of a'b'c 'is 60 * 2 / 3 = 40
ABC perimeter is 40 + 60 = 100

A cylindrical bucket with a bottom radius of 3 decimeters was filled with some water. A section of cylindrical steel with a bottom radius of 10 cm was completely immersed in the water. The water surface in the bucket rose by 3 cm. How long was the steel?
Use the formula

3 decimeter = 30 cm, bottom area of cylindrical bucket = π × R & sup2; π = 3.14 = 3.14 × 9 = 28.26, volume of cylindrical steel = 28.26 × 3 = 84.78, length of steel = 84.78 ^ (π × R & sup2;) = 84.78 ^ (3.14 × 100)

According to the following requirements, fill in the circles from 1 to 20
1. 1 to 20 are prime numbers and odd numbers
2. 1 to 20 are prime numbers and even numbers
3. 1 to 20 are odd and composite
4. Multiple of 12 multiple of 8 common multiple of 12 and 8
5. Factor of 12 factor of 8 common factor of 12 and 8

1.3 5 7 11 13 17 192.2 3.9 15 4.12 multiple: 12 24 36.8 multiple: 8 16 24 32.12 & 8 common multiple: 24.12 & 8 least common multiple: 245.12 factor: 1 23 4 6 12 8 factor: 1 24 8 12 and 8 common factor: 1 24

The unit price ratio of type a raw material to type B raw material is 2:3, and the unit price of type a raw material is 9 yuan after mixing the value raw material of 2000 yuan with type B raw material of 1000 yuan______ ．

Suppose the unit price of a kind of raw material is x yuan, the unit price of B kind of raw material is y yuan, ∵ the unit price ratio of a kind of raw material and B kind of raw material is 2:3, ∵ xy = 23, ∵ y = 32x yuan, according to the meaning of the question: 2000x + 100032x = 2000 + 10009, the solution is: x = 8, through the test: x = 8 is the root of the original equation, so the answer is: 8 yuan

The answers to the mathematical problems of fractional equation in the second semester of junior high school
The calculation method of a water supply company is as follows: if the water consumption is less than 5 cubic meters, it will charge 1.5 yuan per cubic meter. If the water consumption is more than 5 cubic meters, it will charge a higher quota fee. In January, the water consumption of Zhangjia is two-thirds of that of Lijia. The water consumption of Zhangjia is 17.5 yuan per month, and that of Lijia is 27.5 yuan per month. How much is the water consumption exceeding 5 cubic meters per cubic meter?

The water charge exceeding 5 cubic meters is x yuan per cubic meter
5 + 17.5-7.5 divided by x = 2 / 3 (5 + 27.5-7.5 divided by x)
5 + 10 divided by x = 2 / 3 (5 + 20 divided by x)
x=2

Fill in the proper number in the brackets to make the vertical form true
Multiplication:
（ ）（ ）5
（ ）（ ）2
___________________________
6（ ）（ ）
（ ）（ ）（ ）（ ）
___________________________
2 0 （ ） 6 7 0
（）（）9
（）（）（）
______________________
（） 8 （） 6
（）（）（）
（）（）（）
___________________________
8 （） 8 （） 6

1 335 2. 719
×602 ×114
---------- -------------
670 2876
2010 719
---------- 719
201670 ---------------
eighty-one thousand nine hundred and sixty-six

How to solve this problem quickly: 1 / 1 + 1 / 2 + 1 / 3 + 1 / 4 + 1 / 5 + 1 / 6 + 1 / 7 + 1 / 8 =?
How to solve this kind of mathematical problem quickly: 1 / 1 + 1 / 2 + 1 / 3 + 1 / 4 + 1 / 5 + 1 / 6 + 1 / 7 + 1 / 8 =? Is there any quick method

1/1+1/2+1/3+1/4+1/5+1/6+1/7+1/8+1/n=
This sequence is divergent, there is no summation formula, only approximate summation