Math problems, everyone help! A math problem, everyone do me a favor!

1.Set the original length x meters.

then x(1-2 5)+20=x(1+20%)x=100 3

2.There are x parts in total.

Then A is complete (x 4) + 30.

B Complete (x 5) - 15 pcs.

C finish x 2

So (x 4) + 30 + (x 5) - 15 + x 2 = x to get x = 300.

3.Set the barrel height x meters, the oil has 20 x liters.

then 20x(1-3 5)=12

So x = liters.

It's complete!

1.Set the original length of the rope x meters.

1-2/5)x+20=(1+20%)x

3/5x+20=6/5x

3/5x=-20

x=100/3

2.There are x in total.

1/4x+30+1/5x-15+1/2x=x19/20x-x=-15

1/20x=-15

x=3003.Set the original oil x liters.

1-3/5)x=12

2/5x=12x=30

1.Solution: Let this rope be x meters long.

1-(2/5)]x+20=(1+20%)x3/5)x+20=120%x

60%-120%)x=-20

60%x=-20

x=(100/3)

Answer: This rope turned out to be (100 3) meters long.

2.Solution: There are x parts in this batch.

1/4)x+30+(1/5)x-15+(1/2)x=x19/20)x+15=x

19/20)x-x=-15

1/20)x=-15

x=300A: There are 300 parts in this batch.

Decimeter) Answer: The oil in the barrel is high in decimeters.

Is the questioner in the third grade of primary school? I was in the third grade.

.3 meters. If the rope is to be x meters long, then 3x 5+20= Analysis:

After cutting 2/5, only 3/5 of the rope remains, which is 3x 5 long. After connecting another 20 meters, it is 20 percent longer than the original, that is. Unless the data you give is wrong, or the result is meters.

Adding 1/4 to 1/5 gives us 9/20 (less than 2/1), but C has completed 2 points 1, which means that A and B should also have completed 2 points and 1, but from the title we are told that A and B have completed 9/20 and 15. That is, 15 is 1/20 of the total, and the total is 300.

5 decimeters (half a barrel).

From the title, you can know that 12 liters of oil is 2/5 of the oil in the barrel, so the oil in the barrel (half a barrel of oil) has 30 liters (the volume of oil), that is, 30 cubic decimeters. Later, divide the volume by the base area to get the height.

Question 1, 20 meters is equivalent to 20% + 2 5. So 20 (20%+2 5).

Question 2, A, B and C have processed a total of (1 4 + 1 5 + 1 2) = 19 20 and more (30-15) = 15, so 15 is equivalent to 1 20 of the total. So 300 in total.

Question 3, 12 liters equal to 2 of the original barrel of gasoline. So it turned out to be 30 liters of gasoline. Volume Bottom area = height, 30 20 = decimeters.

1 120 2 60 1 (hours).

2 It takes at least X hours for the speedboat to meet the research ship after departing from Island C.

2＋x）×20＝20x＋40, oc＝60√3（20x＋40）²＋60√3）²－2×（20x＋40）（60√3）cos30°

60x) Solve this equation to get: x1 1 x2 13, so it takes at least 1 hour to meet the research ship.

(1) It takes one hour for the speedboat to travel from port B to island C. (The algorithm is simple, think about it yourself, it will help you to answer the same problem next time you encounter it, and you can answer it empirically).

2) The second question is not clear. Did the speedboat go in the same direction after loading supplies on Island C? This is very important!

If the question is a completely independent thought, then congratulations! You have the same level as Master Russell.

For specific explanations, please refer to: Russell's paradox The barber's paradox The third mathematical crisis, which is a good reflection of the shortcomings of Cantor's set theory, which was not better explained until the emergence and development of axiomatic set theory.

There is an axiom zf8 in axiomatic set theory: the regular axiom, which states that all sets are good foundation sets. This axiom directly leads to the fact that it is not permissible to exist such a situation as x belongs to x, so the set mentioned by the subject is not allowed in axiomatic set theory.

Of course, axiomatic set theory has not yet been developed, and the choice of axioms is quite controversial.

A takes x days, B takes x + 3 days. A helps B do it for 2 days, so that B completes it 3 days earlier, and gets 2*[1 x]=3*[1 (x+3)].

x 6 A speed x, which takes 80 x, B speed, 1 hour earlier than the departure of A, 20 minutes, 80 x-1-20 60.

i.e. 80 x 20

The first one is 6 days for A and 9 days for B, and set X for X and D for B.

Two equations 1: x+3=y

2：2/x+2/y+(x-2)/y=1

I didn't see the second one you tried me this (((80-x) x)-1 3)*. If the speed of A is x kilometers per hour, the answer is that the speed of A is 20 km h, and B is 30 km h

After the first cut, the total length is left 1 2;

After the second cut, the total length is 1 2 * 2 3;

After the third cut, the total length of 1 2 * 2 3 * 3 4 remains;

In the same way, after the eighth cut, the total length is 1 2 * 2 3 * 3 4 * 4 5 * 5 * 5 6 * 6 7 * 7 8 * 8 9 = 1 9;

The total length is 1 9 = 1 meter, then the total length is 9 meters.

9 Solution Process: The column equation has x*(1-1 2)*1-1 3)*(1-1 4)*1-1 9)=1 x=9

Set a original x tons and b original y tons. (3/4) x + 1/4)x + y)/4 =90

1 4) x + y) times (3 4) = 90there you go!

Binary Linear Equations.

It turned out that there was grain storage in the B warehouse:

90 (1-1 4) = 120 (tons).

120 1 4 = 30 (tons) 120-30 = 90 (tons) The original A warehouse stored grain: 90 (1-1 4) = 120 (tons).

Use the backwards method.

90 divided by (1-1/4) = 120

A60 divided by (1-1/4) = 80

B 120-80 1/4 = 100