A few simple math problems in elementary school, math problems, everyone can know, so hard to score!

The bottom radius r=4, the perimeter l=2 pa r = is the side length. If the sides are square, then s=a 2, ie.

High, the side is square, then the side area is, the bottom edge is the bottom perimeter is, and the perimeter = 2 pa r, r =, the bottom area is pa r 2=, and the surface area is 2 * bottom area + side area =

Let the bottom circumference l, that is, l is the length of the bottom edge of the side. If you increase it by 1, you will be h+1;Side area s+s=l*h,s+

The solution yields l = and l = 2 pa r

The solution yields r=8, base area, s=pa, r2=

The first question is: 4 times 2 times and so on.

1. A cylinder with a bottom radius of 40cm (the thickness is not mentioned in the title), that is, the circumference of the bottom surface. And because the side view is square, it can be seen that the height of the cylinder is equal to the circumference of the bottom surface. i.e. the side area is.

2. Same as above, it can be seen that the perimeter of the bottom surface is, that is, the radius of the bottom surface is 10 (take. The surface area of the cylinder is .

3. It is easy to know that the side area of the cylinder is the circumference of the bottom surface multiplied by the height. Let the radius of the bottom surface be r and the height be h. If the height increases by 1 centimeter, its side area increases by square centimeters, i.e. (h+1). You can find the base radius. The base area can then be found.

1. The radius of the bottom surface of the circle is 40cm, and because the side view is a square, it can be seen that the height of the cylinder is equal to the circumference of the bottom surface, so the perimeter l=2 pa r = is the side length. If the sides are square, then s=a 2, ie.

2. The side is square, and the circumference of the bottom surface can be known, that is, the radius of the bottom surface is 10 (take. The bottom edge is the circumference of the bottom surface, and the perimeter = 2 pa r, r =, the bottom area is pa r 2=, and the surface area is 2 * bottom area + side area =

3. Let the radius of the bottom surface be r and the height be h. If the height increases by 1 centimeter, its side area increases by square centimeters, i.e. (h+1). l=2 pa r solution yields r=8 base area s=pa r 2=

I didn't have to ask about college, I'm sorry.

The first way: a cylindrical pipe sleeve, the radius of the bottom surface is 4 decimeters, his side view is exactly a square, find his side area? (Keep one decimal place for the number), (to the reason, more detailed), the second way:

The height of a cylinder is centimeters, and its side view is a square, find the surface area of this cylinder? The third way: a cylindrical shape, if the height increases by 1 centimeter, its side area increases by square centimeters, what is the square centimeter of the base area of this cylinder?

First course: Yes. Increasing minus 6 yuan is equivalent to +(-6), which is -6, which is a decrease of 6 yuan, and the second way: b. If it is + (positive) to the east, then the opposite direction of the west to the east is - (minus) and is denoted as -(minus) 10 meters.

Third course: I don't know. The question seems to lack conditions, and it doesn't say which direction is positive, the fourth course:

Master Wang's range has nothing to do with the direction of his driving, 10 meters to the east is counted as 10 meters, and 3 meters to the west is also counted as 10 meters, which is also to consume fuel, not to say that it will consume fuel to the east, and it will not consume fuel to the west. So it doesn't matter if it's positive or negative, just add up all the numbers and multiply them by a. That is, (12 + 3 + 14 + 8 + 10 + 12 + 5 + 8 + 15) multiplied by a, which is equal to 87 times a

The fifth way: indicates that 100 cm is the standard height, but the actual height may have an error of 3 cm, and the actual height may be between 97 cm and 103 cm.

If the height of the desk is 3 lower than the standard height, it is counted as -3

(1): Yes, because +(-6)=-6

2): b is denoted as -10 meters, because if it is positive to the east, it is negative to the west, so it is true.

3): If you still understand it as in the previous question, because it is negative to the west, it is 50 meters to the west.

4) :(12+3+14+8+10+12+5+8+15) A = 87a Because it is fuel consumption, it should be added and then a.

5): It means that if the desk is not standard, the maximum is not more than 103 and the minimum is not less than 97The lower 3 is denoted as -3

I've written so much, it's all my own thoughts, just give me some points.

1, to 2, b, because east and west are in the opposite direction, if east is +, then west is -.

3. To the west, it is generally like this.

4,12+(-3)+14+(-8)+10+(-12)+5+(-8)+15=25 (liters) This is without adding a round trip 5, (1) 3 higher than the standard height and 3 lower. (2) 3 below the standard height is recorded as -3

These are all correct!!

1. Yes, because in general, the increase is represented by +, and the decrease is represented by -; 2. B, because the origin is usually used as the standard; 3. It is impossible to judge without saying the positive and negative; Fourth, it's a bit complicated, pay attention to the round trip; 5. Low 3 is recorded as minus 3

The first lane is written as -10 in the second way, and the third way he travels 50 meters in the opposite direction, and the fourth lane is 87a

Question 1: Choose B

Question 2: 81%.

Question 3: Wrong (the perimeter has changed, but the area has not changed).

Question 4: 112%.

1.Triangles are formed with three wires of equal length, parallelograms and circles compared to them.

a.The circumference is equal and the area is equal.

3.The perimeter is reduced, but the area remains the same.

Original price (1-1 10) (1-1 10) = current price.

That is, the original price 81 100 = current price.

3.The circumference is shortened and the length of the two diameters is missing.

4 112/100 .Past (1+12 100).

1.Right. Because there are countless lines on the axis of symmetry of the circle.

cm, 12 cm wide cuboid paper cut into a circle with a radius of 2 cm, how many can be cut out at most? (I wrote it out in a long formula、Thank you!) ）

Solution: s rectangle s circle = length * width r 2 = 16 * 12 4 = 192 4 15.

Actually: if the diameter is 4, then 12 4 = 3

3*4=12.

In the equation, the remaining ones are also put together to make 15. So realistically, it should be 12.

(1-1 5)-1 5 = meters.

Analysis] Using 1 5 is using 1 5 of the length of the rope, and using 1 5 meters is subtracting 1 5 meters.

2. Not true.

It's so simple. Here's the answer:

Rice. Not necessarily, v [cone] = 1 3 v [bar] v [bar] = 3 * s [cone ] *h [cone ] = s [bar ] * h [bar].

If the cylinder is equal to the base area of the cone, then the cylinder is 3 times the height of the cone, that is:

3 * s [cone] *h [cone] = s [bar] *h [bar] between them can not be equal, equal is just the product, height and base area can not be equal.

Question 1: (The two 1s and 5s in the question do not mean the same thing.) The first is a fraction that means "1 out of 5 is used, and 4 out of 5 remains, i.e., 4 5 remains". There is a "1 5m" is a specific number, which indicates that it was used. ）

Question 2: If the volume of the cone is one-third of the cylinder, then they must be equal in base and height, this statement is true.

1 5 is 1 5 meters to 1 5 meters to get 1 5 meters to 1 5 meters to 1 5 meters to 1 5 meters to 1 5 meters to 1 5 meters to 1 5 meters to 1 5 meters to 1 5 meters to 1 5 meters to 1 5 meters to 1 5 meters to 1 5 meters to 1 5 meters to 1 5 meters to 1 5 meters to 1 5 meters to 1 5 meters to 1

1 5x is how much is used, and (1-1 5)x is how much is left after 1 5.

2.Wrong.

(1): It's rice.

2): Not true.

Question 1 analysis: first 15 meters of 1 5, then it is 15 * 1 5 = 3 meters, 3 meters are used, there are 12 meters left, and 1 5 meters are used, then it is 12 * 1 5 = meters, then it means that the meters are used again, then there are meters left.

15×(1-1/5)（1－1/5）=

The volume of the cylinder = the base area is high.

The volume of the cone = the base area is 3 high

The base area and height can be varied, as long as the result is the same, so it's wrong.

1. Analysis:

5 12 2 = 30 120 30 = 4 The area is enlarged by 4 times, and the edge is enlarged by 2 times, that is: length 12 2 = 24 width 5 2 2 = 5 circumference (24 + 5) 2 = 58 decimeters.

2. Analysis: The ratio of the bottom circumference is 2:3, and the ratio of the bottom radius is 2:3

The ratio of the base area is 4:9

Volume ratio 5:6

The ratio of the high is +1998 2584+2000-2=4582

15 meters, after using one-fifth is 12 meters, and after using one-fifth of the meter, it is used in rice, and there is still (m.) left.

If the volume of the cone is one-third of the cylinder, then they must be equal in base and height, which is not true.

The use of one-fifth and the use of one-fifth mean the same thing.

(1) m.

2. Not true. 3) It's not a meaning. One is used, like eating an apple in your stomach. One is left, like an apple still in hand.

1, m2, no.

3 is a meaning.

1. Set up a large box for x eggs.

2x+6(x-50)=900

8x=1200x=150

150 pcs for large boxes and 100 pcs for small boxes.

2. Set up x chickens.

2x-4(100-x)=20

6x=420x=70

70 chickens and 30 rabbits.

3. There are x chickens.

2x+4(x-20)=100

6x=180x=30

30 chickens and 10 rabbits.

4. Set the first plot of land to be x hectares.

1-2/5)x+(1-5/9)*(72-x)=39x=45

The first plot of land is 45 hectares.

(1) Set x eggs in a large box, then the eggs in a small box are x-50, so: 2x+6(x-50)=900

x=150So: 150 for large boxes and 100 for small boxes.

2.Let the number of chickens be x. The number of rabbits is y

Then: x+y=100

2x-4y=20

So x=70

y=30x-y=20

So x=60

y=304.Let the first plot of land be x and the second plot of land be y

Then: x+y=72

2/5x+5/9y=(90-39)

So x=45

It should be d, and a can be added by one-half plus one-third; b can be added by one-third to one-quarter; And c can be used in half plus quarter plus fifth; But the denominator of the answer to d is ten, which is the least common multiple of two, five, and ten, but no matter how the three are added together, they will not produce nine tenths.

a, one-sixth is equal to one-half plus one-third.

b, 1/22 is equal to 1/2 plus 1/12c, 19/20 is equal to 1/2 plus 1/4 plus 1/5 d, and 9/10 is equal to 1/2 plus 2/5.

So choose D

Answer: d

Analysis: a, 5 6=1 2+1 3;

b、7/12=1/3+1/4；

c、19/20=1/2+1/4+1/5。

Personal opinion: all start from the factor of the denominator of the alternative, for example, the denominator 6 of option A has factors of 2 and 3, and the factor of option B denominator 12 has 2, 3, 4;The denominator of option c 20 has factors of 2, 4, and 5;

The denominator of option d is 10, which has a factor of 2 and 5, and it cannot be calculated as 9 10, I hope it helps you!

The answer is DHere, the three options a, b and c are the most special, the numerators are prime numbers, but 5 6 = 1 2 + 1 3, 7 12 = 1 3 + 1 4, 19 20 = 1 2 + 1 4 + 1 5, and the final d cannot be broken down into the sum of several of the four numbers.

a,5 6=1 3+1 2 If you see that the denominator is six, then you can get the answer by thinking that the denominator can be divided into 6 is 2 and 3.

b,7 12=1 3+1 4 See that the denominator is 12The denominator can be divided into 12 isto try the answer.

c,19 20=1 2+1 4+1 5 See that the denominator is 20The denominator can be divided into 12 isto try the answer.

d, 9 10 = 1 2 + 1 5 + 1 5 In the same way, the result is not true, and the main idea of choosing d is to find the same score according to the denominator, then the answer is clear at a glance.

The main idea of this problem is to convert fractions into the sum of the other four fractions into 1, so.

Therefore d does not match.

a: 5 6=2 6+3 6=1 3+1 2 can be recognized b: 7 12=3 12+4 12=1 4+1 3 can be recognized c:

19 20 = 4 20 + 10 20 + 5 20 = 1 5 + 1 2 + 1 4 can be recognized.

d: 9 10 = 2 10 + 2 10 + 5 10 = 1 5 + 1 5 + 1 2 Because there are two 1s and 5s, they cannot be recognized.

So the correct answer is d