Ask everyone a math problem in the first year of junior high school to solve it with a binary inequa

1.Solution: Set the purchase price to X yuan.

then 150-x>=, and the solution is x<=136

150-x<=, which gives x>=125

Therefore, the purchase price range is 125-136 yuan.

2.Solution: Set type B to pump in 20 minutes, and pump x tons of water more than A.

Then the solution is x=ton.

Set type B to pump in 22 minutes, and pump x tons of water more than A.

Then the solution is x=ton.

So B pumps about tons more water per minute than A.

3。If you take 60mg, the dosage is 60 4--60 3, both 15--20mg, if you take 120mg, the dosage is 120 4--120 3, both 30--40mg, so the dosage is between 15--40mg.

1.Set the purchase price to $x.

then 150-x>=, resulting in x<=136

150-x<=, resulting in x>=125

Therefore, the purchase price range is 125-136 yuan.

2.Type B will be pumped in 20 minutes, pumping x tons more water than A.

Then so x=t.

Assuming that type B is pumped in 22 minutes, it will pump x tons of water more than A.

Then so x=t.

So B pumps about tons more water per minute than A.

3。If 60 mg is taken, the dosage is 60 4--60 3, i.e. 15--20 mg, if 120 mg is taken, the dosage is 120 4--120 3, i.e. 30--40 mg, so the dose is between 15--40 mg.

* Hee-hee-hee ......, embarrassed to complete the task.

Solution: 3x+a=x-7

3x-x=-7-a

2x=-7-a

x=-(7+a)/2

Since the root is a positive number, so.

7+a)/2>0

7+a)>0

7-a>0

a<-7

The value range of a is a<-7

x-(x/2+x/4+x/7)=6

x(1-1/2-1/4-1/7)=6

x(1/4-1/7)=6

x(7-4)/28=6

x=168/3=56

A total of 56 students participated in this extracurricular activity.

Solution, a total of x students participated in extracurricular interest activities this time.

x-(x/2+x/4+x/7)=6

x=56A, a total of 56 students participated in the extracurricular interest activities.

If you make at least x per day, you can get the inequality of 42 + (4-1) x 240 x 66

In the future, it is necessary to make at least 66 ribbons every day on average, so as to complete the work of Ren Que Fan on time or in advance.

240-42 = 198, Hengqing search because it took 1 day, so there are only 3 days left.

Therefore, on average, it takes at least 198 3 = 66 per day to complete the task as required or ahead of schedule.

Suppose it takes x days to complete. It's already been used for a day, so there are (x-1) days left to complete the streamer making. Make at least Y ribbons every day, and the column formula is:

240-42-（x-1）*y=0 。When you do the question, you just change the x to the time given in the question. Thank you, hope it helps.

The condition of the total number of days is missing, and it is not possible to columnize it.

Subtract 42 from 240 to calculate how many streamers need to be made (240-42=198), then divide this number by time (you don't have time here) and you're good to go.

The plan is to be completed in n days, 42 streamers will be made on the first day, and an average of m streamers per day will be made thereafter.

then 1+(240-42) m n 1+198 m n

If you have at least Y ribbons made every day when you accept the assignment and there are x days before the festival, then Y (240-42) (X-1) 198 (X-1).

After that, an average of at least x ribbons should be made every day.

240-42）/x≤4-1

x≥66

Please indicate when you want it to be done.

x people. There is a total amount of money) <

Just solve it.

Because both sides are divided by 3-2k at the same time, it becomes x 1, so 3-2k 0

So k three-two.