Ask a few practical problems. Elementary school fifth grade. Very simple wow, can make a few is a few. (can only use equation set X and formula solution) 1. Party A and Party B walk from two places 48 kilometers apart. Party A walks 5 kilometers per hour, and Party B starts four hours later. After another two hours, they meet and ask Party B how many kilometers per hour? 2. A and B start from two places at the same time and travel in opposite directions. It is known that car a travels 45 kilometers per hour, Car B travels 32 kilometers per hour. When it meets, car a travels 104 kilometers more than car B. how many kilometers is the distance between the two places? 3. The stadium is 400 meters long. Xiao Zhang and Xiao Lin run in the same direction on the same ground at the same time. If Xiao Zhang runs 11 meters per second and Xiao Lin runs 9 meters per second, how long does it take when they first meet? If they run in the opposite direction at the same time, how long does it take when they first meet? 4. A and B run from ab at the same time. A runs 48 kilometers per hour and B 36 kilometers per hour. The two cars meet at 24 kilometers from the midpoint. How many kilometers is the distance between AB and B? 5. The speed of a is 8 m / s, and that of B is 5 m / s. at the start, B stands 15 meters in front of a and asks if a has overtaken B after a few seconds? 6. On the highway, a bus is driving forward at the speed of 65 km / h, and there is a car coming 15 km behind it. How many km must the car drive per hour if it wants to catch up with the bus in 7.5 hours? 77. I've already said it's simple. Just do it.

1. [(48-5 * 4) / 2] - 5 = 9 (km)
2. [104 / (45-32)] * (45 + 32) = 616 (km)
3.400 / (11-9) = 200 (seconds) 400 / (11 + 9) = 20 (seconds)
4.24 * 2 / (48-36) * (48 + 36) = 336 (km)
5.15 / (8-3) = 5 (seconds)
6.65 + 15 / 7.5 = 67 (km)

It can be solved by equation and formula
If the upper bottom of a trapezoid is increased by 2 cm and the lower bottom is decreased by 2 cm, then it becomes a square with a side length of 5 cm. What is the area of the trapezoid?

Upper bottom: 5-2 = 3 (CM) lower bottom: 5 + 2 = 7 (CM) height: 5 (CM) (height is one side of the square) area: (3 + 7) × 5 △ 2 = 25 (square cm) (trapezoidal area: (upper bottom + lower bottom) × height △ 2)
A: the area of trapezoid is 25 square meters

Write the formula and the reason
1. The tractor ploughed a piece of land. In the morning, it ploughed two fifths of the fast land. In the afternoon, it ploughed one fifths of the hectare. There are still seven tenths of the hectare left uncultivated?
2. Two passenger and freight cars run in the opposite direction from the center of a and B at the same time. After a period of time, the bus arrives at B, and the truck is 30 kilometers away from A. It is known that the speed of the truck is three fourths of that of the bus. How many kilometers are there between a and B?

1. X hectares
2/5*x+1/5=7/10
Multiply both sides by 10
4x+2=7
x=5/4
Suppose the speed of the freight car is 3x, the speed of the bus is 4x, and the time for the bus to arrive at destination B is t
yes:
3x * t = whole journey - 30
4X * t = whole journey
It can be known by subtracting the two formulas
x*t=30
Then the whole course = 4 * (x * t) = 120

Write the formula and explain the reason
1. There is a rectangular stone, 5.3 decimeters in length and 3 decimeters in width. During processing, the length, width and height are chiseled out by 0. If each cubic decimeter stone weighs 2.7 kg, how many kg does the stone weigh after processing?
2. A rectangular glass goldfish tank (no cover), 25 cm wide and 40 cm high. How many square decimeters does it need to make this goldfish tank? How many liters can this goldfish tank hold
3. A warehouse is 18 meters long, 12 meters wide and 5 meters high, and 40% of the warehouse volume of the cargo station. If the average weight of goods per cubic meter is 5400 kg, how many kg are the goods in the warehouse?
4. Forge a 6 cm square billet into a 12 cm wide and 6 cm cuboid part. What is the height of the part?

1: 40.5kg
2: 72.5 square decimeters, 50 liters
3: 18 * 12 * 5 * 40% * 5400 = 2452800kg
4: 6 * 6 * 6 / 12 / 6 = 3cm

There are seven different natural numbers, and the difference between at least two of them is a multiple of 6. Why? Formula and reason

The remainder of a number divided by 6 is 0, 1, 2, 3, 4 and 5. If there are 7 different natural numbers, there must be two numbers divided by 6. The difference between the two numbers is a multiple of 6

Take at will______ The difference between at least two numbers is a multiple of 7

The remainder of natural number divided by 7 is: 0, 1, 2, 3, 4, 5, 6, so 7 divides natural number into 7 categories, that is: dividing by 7 is more than 0, 1, 2, 3, 4, 5, 6, so it can be regarded as 7 drawers, at least 8 numbers, there must be two numbers in one drawer, and the remainder of these two numbers divided by 7 is the same

A natural number, 3 divided by less one, 5 divided by less three, 7 divided by less five?
Thank you, brothers and sisters I'm in a hurry
Do me a favor

The natural number minus 2 can be divided by 3, 5 and 7 at the same time
The minimum of this natural number is the least common multiple of 3, 5 and 7 + 2:
3. The least common multiple of 5 and 7 is 3 × 5 × 7 = 105,
The minimum natural number is 105 + 2 = 107

Write three different non-zero natural numbers, at least two numbers can be selected. The difference between the two numbers is a multiple of 2. Why?

Because of three different nonzero natural numbers, at least two of them are even or odd, and the difference between any two even or odd numbers is a multiple of 2

In any six different non-zero natural numbers, the difference of at least two numbers is a multiple of 5. Why?

The remainder of a natural number divided by 5 has five cases: 0, 1, 2, 3 and 4
Take them as five drawers and put six natural numbers in them,
At least two will be in the same drawer,
Then the difference between the two numbers must be divisible by 5, because the remainder of their division by 5 is the same, and the remainder will be eliminated after subtraction. Therefore, the remainder of the difference divided by 5 must be 0, which is a multiple of 5

There are six non-zero natural numbers, and the difference between at least two of them is a multiple of 5. Why?

How does the drawer work
Because a positive integer is divided by 5, there are five possibilities for the remainder, namely 0, 1, 2, 3, 4
The remainder of two numbers divided by 5 is the same
Then the difference between the two numbers can be divided by 5
If there are five non-zero natural numbers, the difference between them is not a multiple of 5
Then they divide by 5 and the remainder is 0, 1, 2, 3, 4
So, the sixth number, no matter what the remainder is divided by 5, is the same as one of the previous five numbers
Then the difference between the two numbers is a multiple of 5
Therefore, the proposition is proved

It can be solved by equation and formula If the upper bottom of a trapezoid is increased by 2 cm and the lower bottom is decreased by 2 cm, then it becomes a square with a side length of 5 cm. What is the area of the trapezoid?