In a box, there are 20 balls in red, yellow and blue, each with at least a few balls, so that two pairs of balls in the same color can be guaranteed? At least how many balls can be written Then, three pairs of balls of the same color can be guaranteed? Four pairs? What rules do you find? (the so-called ball of the same color refers to two balls in each team of the same color, not all the balls taken out of the same color)

In a box, there are 20 balls in red, yellow and blue, each with at least a few balls, so that two pairs of balls in the same color can be guaranteed? At least how many balls can be written Then, three pairs of balls of the same color can be guaranteed? Four pairs? What rules do you find? (the so-called ball of the same color refers to two balls in each team of the same color, not all the balls taken out of the same color)

20+20+1+1

How many square meters is one square foot

3 feet = 10 meters
Therefore, 1 Zhang = 10 / 3M
So 1 square foot = 100 / 9 square meters

1. Uncle Li raised 200 chickens this year, three seventh more than last year. How many chickens did he raise last year?
2. The largest pyramid in Egypt, due to the erosion of wind and rain, is now only 140 meters high, which is 21 times lower than when it was built. How many meters is the height of this pyramid when it was built?
3. A car from a to B, has been three fourths of the whole journey, more than 60 kilometers, find the distance between a and B
I want the formula! I'd better talk about the solution

1.200÷(1 + 3/7)
=200×7/10
=140 pieces
A: 140 chickens were raised last year
2.140÷(1 - 1/21)
=140×21/20
=147 (m)
A: the pyramid was 147 meters high when it was built
3.60÷（3/4 - 1/2）
=60×4
=240 (km)
A: the distance between a and B is 240 km

What's the formula
1. For two bundles of wires with the same length, the first bundle takes 60 meters, and the second bundle takes 90 meters. The remaining length of the first bundle is 1.5 times that of the second bundle. How long are the two bundles of wires?
There are three classes a, B and C in the fifth grade of Shuren primary school. There are 49 students in class A and B, 52 students in class B and C, and 53 Students in class A and C. how many students are there in the three classes?
3. When Jiajia calculates 2.91 divided by a number, because the decimal point of the quotient moves one place to the right, the result is 23.5
4. The two cars start from the two cities 1230 kilometers away, and travel in opposite directions. Car a travels 55.4 kilometers per hour, and car B travels 47.1 kilometers per hour. After a few hours, the two cars meet?
5. The machine tool factory has to process 2480 parts. The original plan is to process 100 parts a day. After 20 days, it will process 120 parts a day instead. How many days can the task be completed?

1. Let the wire length x, (X-60) * 1.5 = (x-90) 2. Let a, B and C be x, y, ZX + y = 49y + Z = 52X + Z = 53, and then add x, y and Z. 3. The decimal point of quotient is shifted one place, and the original result should be 2.35. Divide 2.91 by 2.35. 4.1230 / (55.4 + 47.1) 5.2480-100 * 20 is 20 days later, and then divide the rest by 120

How many liters is a cubic meter of air equal to?
Do you mean the air in the air?

1 liter = 1 cubic decimeter
1000 cubic decimeter = 1 cubic meter
So 1 cubic meter = 1000 liters

A mathematics problem, the first day of junior high school textbook (Zhejiang Education Edition) page 33, question 5, see the supplementary explanation for details, high score reward ah
As shown in the figure, △ ABC is an equilateral triangle. Extend Ca, AB, BC to a ', B', C ', respectively, so that AA' = BB '= CC'. Is △ a'b'c 'an equilateral triangle? Please explain the reason

Because = BB '= CC', AC + AA '= BC + CC' = AB + BB ', namely a'c = BC' = ab ', angle a'cc' = angle a'ab '= angle b'bc'
So triangles a'cc ', a'b'a, b'bc' are congruent
Therefore, ca'c '+ b'a'a = - a'b'a + - bb'c' = - a'c'c + - b'c'c
So the three angles of a triangle add up to 180 degrees
So ∠ b'a'c '= a'c'b' = a'b'c '
So, △ a'b'c 'is an equilateral triangle

3+6+9+12+.+96+99=?
Please use the thinking of the fourth grade of primary school to solve the problem?

If front + 0, then 0 + 3 + 6 + 9 +. + 99 = (0 + 99) + (3 + 96) + (6 + 93) +. + (48 + 51) has 17 groups, then the result is 16 * 99 = 17 * (100-1) = 1700-17 = 1683

Four eights plus appropriate operation symbols result in 0, 1, 2, 3

8×8-8×8=0
8×8÷8÷8=1
8÷8+8÷8=2
(8+8+8)÷8=3

Feedback on learning mathematics in class

Let the speed of this truck be XKM / h
15|3600（3.6+X)=17|3600(X-3.6）
X=67.6
A: the length of the train is 6760m

Simple operation of 12 × 36 + 12 × 63 + 12?

12×36＋12×63＋12
=12×（36+63＋1）
=12×（36+64）
=12×100
=1200