Math problems are urgent, and there is a reward for answering well

I'll just write you the sum of the equations, and if you need the idea and the solution of the equation, then ask me the one you can't figure out.

The original salt of a bottle of brine is one-eleventh of water, after adding 15 grams of salt, the salt accounts for one-ninth of the brine, how many grams of the original brine in the bottle?

Solution: If the original salt water x, then there is 10x water

x+15)*9=(x+15)+10x

x = 60 (grams).

Original salt water = original water Original salt 60 * 10 + 60 = 660 (grams).

Two barrels of oil A and B, a barrel of oil is heavier than B barrel of oil, after pouring out grams from each of the two barrels of oil, five-tenths of the twenty-first of a barrel is equal to one-third of a barrel B, how much does the two barrels of oil of A and B weigh respectively?

Solution: If the original weight of the first barrel of oil is x grams, then the original weight of the second barrel of oil is grams.

x=18, so barrel A of oil originally weighed 18 grams, and barrel B of oil originally weighed grams.

Processing a batch of parts, originally planned to process 30 per day, when the processing of one-third, due to the improvement of technology, the work efficiency increased by 10 percent, the result was completed 4 days ahead of schedule, how many parts are there in this batch?

Solution: There are x parts.

x/30-4=(x*1/3)÷30+(x-x*1/3)÷(30+30*10%)

x=1980 (pcs).

If two cars A and B drive out of A and B at the same time, they will go in the opposite direction. You can meet you on the way after 4 hours. It is known that the speed ratio of car A and B is 3:

4. At this speed, if the two cars have to meet at the midpoint of A and B. How many hours in advance should car A depart?

Solution: The car should be set out x hours in advance.

4*(3+4)/2=3*(14/4+x)

x=1 and 1 6

That is, A should be opened 1 hour and 10 minutes in advance.

1,000 kilograms of fruit with a moisture content of 99 percent were transported to the warehouse, and a week later it was found that the water content had been reduced to 98 percent.

Solution: Let's say that this batch of fruits weighs x kilograms.

1000-1000*99%=x-x*98%

x = 500 (kg).

Two cars A and B travel in the opposite direction from the two places at the same time, and then the two cars meet at a distance of 20 meters from the midpoint, and it is known that the speed of A is three-quarters of that of B, and the speed of car B is obtained.

If B's velocity is x, then A's velocity is 3x 4

x=64(m-h).

Hello, 1After one salt addition, the water remains unchanged, and the condition in the question can be changed to the score of salt to water.

1 11-1 =1 10 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1

So water + salt = 600g + 60g = 660g

First, find the 5 consecutive 2s that appear for the first time 221222223 and then calculate how many numbers the first 2 is.

Before 221, 3 digits 100-221 have a total of 221-100+1=122 including 122*3=366 numbers.

2 digits 10-99 There are 90 in total, including 90*2=180 numbers, 1 digit has 1-9 9.

So 221 is preceded by 366 + 180 + 9 = 555 digits (including 221), so from the 556th digit there are 5 consecutive 2s

Eric is right, it has to be counted from the first few numbers, and the questions have to be carefully reviewed.

The first occurrence of 5 consecutive 2s is in 221222223, and then the first 2 of the 5 consecutive 2s here is calculated as the first number:

The 3 digits before 222 are 100-221, which contains a total of 122*3=366 digits;

The two-digit number is 10-99, which contains a total of 90*2=180 digits;

1 digit has 1-9, 9 digits;

So 222 is preceded by 366+180+9=555 digits, so from the 556th digit there are 5 consecutive 2s

………221）（222）（223）

1 9 has 9 1 digits, 10 99 has 90 2 digits, and 100 221 has 122 3 digits.

9*1+90*2+122*3=555, which means that there are 555 numbers before this 2, so this 2 is the 556th number.

A is six-fifths of what has been gained, then B is five-fifths of B, and B + 5kg = six-fifths of B (A).

So 5kg = 1/5 of B.

So B is 25kg, A is 25 six-fifths = 30kg

Let B be the original x

Then the original X*6 5

Now after homogeneity, B has x+5, and A has x*6 5-5, so there is: x+5=x*6 5-5

The solution is: x=50 (kg), x*6 5=60 (kg), that is, 60 (kg) for the original A and 50 (kg) for the original B

After A gives B 5kg, A and B are equal, then A is 5*2=10kg more than B

And this 10kg is the original (6 5-1) = 1 5So B originally had 10 (1 5) = 50kg, and A originally had 50 + 10 = 60kg

Solution: 80ml=80cm, the volume of each extrusion is ·, then the volume of one day of extrusion is, so the number of days that this facial cleanser can be used is 80 days), so it can be used for up to 100 days.

-4<=x<5

x<0 or x>1 2

x=2,y=0 or x=10 3,y=4 10x=y=0

x = plus or minus root number 3, y = plus or minus 1

Constant -2 times root number 3 = 2 or x< = -2

x>2 or x< = root number 3

x<7,x≠2

These are all very basic questions, why don't you do it yourself?