Beginning with equation problems, first year of junior high school questions about equations

Let the ten digits be x and the single digit be x+5

x>0,x+5<10.

x<510x+x+5>4(x+5);;10x+x+5<=5(x+5)11x+5>4x+20;;;11x+5<=5x+257x>15;;;6x<=20

x>2;;;x<=3

x=3x+5=8

The two-digit number is 38

Solution: Let the ten digits of this two-digit number be x, then the single digit of this two-digit number is (x+5)4(x+5) 10x+(x+5) 5(x+5)15 7 x 10 3

Because x is an integer.

So x=3 then x+5=8

A: This two-digit number is 38

Untie. Let it be (10x+(x+5)) i.e. ten bits x, and single digits (x+5) have. 4(x+5)<10x+(x+5)<=5(x+5)4x+20<11x+5<=5x+25

Solve the left x>15 7

The right part of the solution x<=10 3

so 15 7 x is an integer.

so 2so x=3

This number is 38

The number on the tens is set to a

The number in the single digit is b

This number = 10a + b

So b-a=5, b=a+5;

This two-digit number is more than 4 times the number in its single digit, but not more than 5 times the number in its single digit, so 5b>10a+b>4b; Substituting gets: 5a+25>10a+5>4a+20, so 4>a>;

So a=3, b=8

The number of the five digits greater than the ten digits is 16, 27, 38, and 49, while the number that satisfies the latter condition is only 38

Let the number of tens be x single digits x + 5

4（x+5）≤10x+（x+5）≤5（x+5）

x=3 for 38

Solution: When "visiting neighbors only once" is understood as "a family visits only one neighbor", the answer is that there are 54 households in this village.

Second explanation: When "visiting a neighbor only once" is understood as "a family visits a neighbor only once", then a family has two neighbors and visits twice, while two households on both sides have only one neighbor and can only visit once. From this, there can be x households in the middle.

In addition, two families on both sides visited twice.

then 2+2x=54

2x=52x=26

Add two households on both sides, then 26 + 2 = 28

The village has 28 households.

Suppose there are x households, and the two households at both ends visit only once, and the households in the middle are both twice, so there is an equation.

2+2（x-2)=54

2x-2=54

2x=56x=28

A: There are 28 households in total.

The question you are asking is not clear and difficult to understand.

Donkeys and mules walked side by side in the streets, each carrying several parcels. The donkey complained that his master had put too much weight on him, but the mule said, "Brother, your burden is not too heavy!"

Behold, if the one that is taken from your back were to me, my burden would be twice as heavy as thee; And if you take the package from my back, you will be the same burden as I do. ”

Now donkeys and mules are each carrying x, y packages, and then the formula is: y+1=2(x-1) y-1=x+1. How is it calculated?

y+1=2(x -1 ) y-2x=-3 ①y-1=x+1 y-x=2 ②

Obtain: -x+2x=2-(-3).

x=5y=7

1.He rode from his home half an hour later and found that there was not enough time, so he increased his speed to twice as much, and arrived at Zhouzhou's home on time half an hour later. It is known that their homes are 30 kilometers apart, so they follow the original cycling speed.

Solution: Let the original speed of the follower be x kilometers per hour.

x=20 2.A work, A alone needs 15 days to complete, B alone needs 12 days to complete, this work is done by A and B, and B rests for 7 days during the construction period, how many days to complete?

It takes x days to complete.

From the question: A completes 1 15 every day B completes 1 12 every day to get the equation: 1 15*x+1 12*(x-7)=1, and then solves: x=

Therefore, it takes 11 days to complete.

3.A work is completed in 20 hours by A alone, and 12 hours by B alone.

If A does it alone for 4 hours, and A and B do the rest together, Q: How many hours does it take to complete?

Solution: It takes x hours.

4/20+1/20x+1/12x=1x=

The original length of this strap is x centimeters.

x-1)=1/3x-4

x=45The original length of this strap is 45 cm.

The rope is folded in half twice, and the resulting length is 1 4

48cm

There are too many problems, it is not easy to list them one by one, just on the problem of train driving, the following question is an example to illustrate:

How long does it take for a train to cross a 250-meter-long tunnel and a 210-meter-long iron bridge in 23 seconds, and another 320-meter-long train with a speed of kilometers per hour?

Analysis: The train itself has a certain length, whether the train crosses a bridge or a tunnel, the front of the locomotive enters and the tail exits before it is considered to be completely passed; The process of taking the wrong car is equivalent to the time taken by the two cars when the front of the car meets until the rear of the car meets again, that is, the time taken by the sum of the speeds of the two cars to pass the sum of the two car lengths;

From "a train passes through a 250-meter-long tunnel in 25 seconds, and it takes 23 seconds to pass through a 210-meter-long iron bridge", it is known that the body length and speed of a certain train are set to x and y respectively, then there are 25y=250+x, 23y=210+x, and the solution is x=250m, y=20m s, that is, the body length and speed are 250m and 20m s, respectively;

From "the train is wrong with another train with a length of 320 meters and a speed of kilometers per hour", the body length and speed of the train are 320m and 18m s respectively, then t=(250+320) (20+18)=15s is the wrong train time;

You can find the corresponding questions for other questions, I will help you answer them one by one, all problems can not be solved at one time).

Suppose a piece of clothing ** is p, 12 months in a year, then every month he is paid (p+10) 12, then for seven months he deserves 7*(p+10) 12, so.

7*(p+10) 12=p+2, which gives p=, so the garment should be worth a silver coin.

If the first two warehouses are x tons, then the first warehouse is 3x tons, and after taking them out and putting them in, there is the following equation.

5/7（3x-20）=x+20

Solution x=30

Set x days after the two teasing as much, know the rent rules.

200-15x=80+25x

Solution x=3

Let the second warehouse of the dismantling circle have grain x, then the first warehouse of the first warehouse of the first warehouse has 3x and has the equation: (3x-20) multiplied by 5/7 = x+20 to solve. After the y-day set, both warehouses had as much coal.

200-15y=80+25y

Solve and get it.

x 2 - y 3 = 1, take x = -2, then -2 2 - y 3 = 1, y -6

x 2 - y 3 =1, take x = 1 2, 1 2 2 - y 3 =1 y -9 4

Two sets of solutions to a system of equations.

x = -2,y＝-6

x = 1/2 y＝-9/4