In the first volume of the seventh grade, find 50 arithmetic problems and their answers, 10, and the rest with scores should have more than 4 numbers.

25x+y= 1200

Answer: x=48 y=47.

(2) 18x+23y=2303

74x-y= 1998

Answer: x=27 y=79

(3) 44x+90y=7796

44x+y=3476

Answer: x=79 y=48

⑷76x-66y = 4082

30x-y=2940

Answer: x=98 y=5 1.

(5) 67x+54y=8546

7 1x-y=5680

Answer: x=80 y=59

(6) 42x-95y=- 14 10

2 1x-y= 1575

Answer: x=75 y=48

(7) 47x-40y=853

34x-y=2006

Answer: x=59 y=48

(8) 19x-32y=- 1786

75x+y=4950

Answer: x=66 y=95

(9) 97x+24y=7202

58x-y=2900

Answer: x=50 y=98

( 10) 42x+85y=6362

63x-y= 1638

Answer: x=26 y=62

( 1 1)85x-92y =-25 18

27x-y=486

Answer: x= 18 y=44.

( 12) 79x+40y=24 19

56x-y= 1 176

Answer: x=2 1 y= 19.

( 13) 80x-87y=2 156

22x-y=880

Answer: x=40 y= 12.

( 14) 32x+62y=5 134

57x+y=2850

Answer: x=50 y=57

( 15) 83x-49y=82

59x+y=2 183

Answer: x=37 y=6 1.

( 16) 9 1x+70y=5845

95x-y=4275

Answer: x=45 y=25.

( 17) 29x+44y=528 1

88x-y=3608

Answer: x=4 1 y=93.

( 18) 25x-95y=-4355

40x-y=2000

Answer: x=50 y=59

( 19) 54x+68y=3284

78x+y= 1404

Answer: x= 18 y=34.

(20) 70x+ 13y=3520

52x+y=2 132

Answer: x=4 1 y=50.

(2 1) 48x-54y=-3 186

24x+y= 1080

Answer: x=45 y=99

(22) 36x+77y=76 19

47x-y=799

Answer: x= 17 y=9 1.

(23) 13x-42y=-27 17

3 1x-y= 1333

Answer: x=43 y=78

(24) 28x+28y=3332

52x-y=4628

Answer: x=89 y=30

(25) 62x-98y=-2564

46x-y=2024

Answer: x=44 y=54.

(26) 79x-76y=-4388

26x-y=832

Answer: x=32 y=9 1.

(27) 63x-40y=-82 1

42x-y=546

Answer: x= 13 y=4 1.

(28) 69x-96y=- 1209

42x+y=3822

Answer: x=9 1 y=78.

(29) 85x+67y=7338

1 1x+y=308

Answer: x=28 y=74

(30) 78x+74y= 12928

14x+y= 12 18

Answer: x=87 y=83.

(3 1) 39x+42y=533 1

59x-y=584 1

Answer: x=99 y=35

(32)29x+ 18y = 19 16

58x+y=2320

Answer: x=40 y=42

(33) 40x+3 1y=6043

45x-y=3555

Answer: x=79 y=93

(34) 47x+50y=8598

45x+y=3780

Answer: x=84 y=93

(35) 45x-30y=- 1455

29x-y=725

Answer: x=25 y=86

(36) 1 1x-43y =- 136 1

47x+y=799

Answer: x= 17 y=36.

(37) 33x+59y=3254

94x+y= 1034

Answer: x= 1 1 y=49.

(38) 89x-74y=-2735

68x+y= 1020

Answer: x= 15 y=55.

(39) 94x+7 1y=75 17

78x+y=3822

Answer: x=49 y=4 1.

(40) 28x-62y=-4934

46x+y=552

Answer: x= 12 y=85.

(4 1) 75x+43y=8472

17x-y= 1394

Answer: x=82 y=54.

4 1x-38y =- 1 180

29x+y= 1450

Answer: x=50 y=85

(43) 22x-59y=824

63x+y=4725

Answer: x=75 y= 14.

(44) 95x-56y=-40 1

90x+y= 1530

Answer: x= 17 y=36.

(45) 93x-52y=-852

29x+y=464

Answer: x= 16 y=45.

(46) 93x+ 12y=8823

54x+y=49 14

Answer: x=9 1 y=30.

(47) 2 1x-63y=84

20x+y= 1880

Answer: x=94 y=30

(48) 48x+93y=9756

38x-y=950

Answer: x=25 y=92

(49) 99x-67y=40 1 1

75x-y=5475

Answer: x=73 y=48

(50) 83x+64y=929 1

90x-y=3690

Answer: x=4 1 y=92.

Party A and Party B walk in opposite directions, with a distance of 36 kilometers. If Party A leaves before Party B at 2 o'clock, they will meet after Party B leaves at 2.5 o'clock. If B leaves at 2 o'clock before A, then they meet after A 3. How many kilometers do A and B walk per hour?

Solution: Suppose two people, A and B, walk at the speed of X kilometers and Y kilometers per hour respectively. According to the meaning of the question:

4.5x+2.5y=36 x= 6

3x+5ky=36 Solve this equation and you can get: y=4.

So A walks 6 kilometers per hour and B walks 4 kilometers per hour.

The distance between the two docks is 60 kilometers, so it takes three hours for a ship to go back and forth between the two places, and four hours for a ship to go upstream, so as to find out the speed and current speed of the ship in still water. ②

Analysis: review the relationship between ship speed and ship speed and current speed in still water during downstream navigation and countercurrent navigation.

Ship speed sailing downstream = ship speed in still water+current speed.

Countercurrent speed = ship speed in still water-current speed

Teachers and students analyze two equal relations together.

(1) downstream sailing speed × 3 = 60km.

⑵ Countercurrent sailing speed × 4 = 60km.

Solution: Let the speed of the ship in still water be X km/h and the current speed be y km/h. ..

3(x+y)=60 ① Judging from the meaning of the question.

4(x-y)=60 ②

Solve this equation group; get

x= 17.5

y=2.5

A: Omit.

Exercise: P48 7.

The distance between the two places is 20 kilometers. A starts from place A and place B at the same time and moves in opposite directions. They will meet at point c in two hours. After meeting, A quickly returns to A, and B still advances to A. When A returns to A, B is 2 kilometers away from A, so find the speed of A and B..

Student activities: analyze, think and find equal relations independently, and be performed by a student.

Solution: let a speed be x kilometers per hour and b speed be y kilometers per hour. According to the meaning of the question,

2(x+y)=20 ①

2x-2y=2 ②

solve

x=5.5

y=4.5

Answer: A speed is 5.5 kilometers per hour, and B speed is 4.5 kilometers per hour.

Both parties drive in the same direction from point C, and the time for Party A to return to point A is 2 hours. At the same time, Party B arrives at Point D, which is 2km away from Point A, so we can get the equality relation:

Travel-Travel = 2km

35. The distance between 35.B and B is 5 kilometers. A car and a bike go from A to B at the same time. When the car arrives at point B, the bike will complete the journey. After stopping in B for half an hour, the car returned to A at the original speed and met the bike 24 minutes later. Find the speed of cars and bicycles.

Analysis: According to the car, the bicycle will not complete the journey until it reaches point B. The speed of the car is four times that of the bicycle. The remaining distance is equal to the distance of cycling for half an hour plus 24 minutes plus the distance of car driving for 24 minutes. The total length of the distance between a and b is known. As long as the speed of bicycle and car are set to X km/h and Y km/h respectively, the equation can be listed.

Solution: let the speed of the bicycle be x km/h.

The speed is y km/h.

Establish an equation according to the meaning of the problem:

To solve this system of equations:

Answer: The bicycle speed is 15km/h, and the car speed is 60 km/h. ..

When the Young Pioneers arrived at the summer camp school, they went down the mountain first and then took the smooth road. A young pioneer rode a bicycle at a speed of 12 km per hour.

Down the mountain, I crossed the flat road at a speed of 9 kilometers per hour. It took me 55 minutes to get to school. The speed of crossing the road is not good when I come back.

But it took 1 hour and 10 minutes to get back to the camp at a speed of 6 kilometers per hour. I asked if the summer camp had arrived at school.

How many kilometers?

Analysis: The journey is divided into two sections, a flat road and an inclined road. The round trip is the same, but the change from top to bottom leads to the time difference.

Similarly, so let the length of the flat road be x kilometers and the length of the slope be y kilometers, indicating the time, and use two different flow sequences.

Two equations form a set of equations.

Solution: Let the leveling road be x kilometers long and the slope road be y kilometers long.

Set the equation according to the meaning of the question:

To solve this system of equations:

After investigation, it conforms to the meaning of the question.

x+y=9

It is 9 kilometers from the summer camp to the school.

Express length168m, slow length184m. If two cars face each other, it takes 4 seconds to meet and leave. If driving in the same direction, it takes 16 seconds to catch the local train and leave. Find the speed of two cars.

Analysis: If two cars drive in the opposite direction, their relative speed is the sum of speeds; If two cars travel in the same direction, their relative speed is the difference of speed, but the relative moving distance is the sum of the lengths of the two trains.

Solution: Let the express speed be X km/h and the local speed be Y km/h, and the equations can be obtained according to the analysis.

A: The express train travels 55 kilometers per hour, and the local train travels 33 kilometers per hour.

The ratio of the remaining two corners is 2:3. How many degrees are these two angles?

Analysis: The two angles are complementary, and the sum is 90. Solution: Let two complementary angles be 2x and 3x respectively. 2x+3x = 90°

X = 18 2x = 36 3x = 54 A: the two angles are 36 and 54 respectively.

The difference between the complementary angle of 40 and its complementary angle is a right angle. Find the degree of this angle.

Analysis: Let this angle be x, then the complementary angle of this angle is (180-x), and the complementary angle of this angle is (90-x).

Solution: Set this to X, and then

( 180-x)-2(90-x)=× 180

x=60

A: This angle is 60 degrees.

-25+49=49-25=24

138+(-73)= 138-73=65

-33-67=-(33+67)= 100

-245-87+29=-(245+87-29)=-303

38-47+85=85+(38-47)=85-9=76

149+23-37=23-( 149+37)=23- 186= 163

44-64+74-94=(44+74)-(64+94)= 1 18- 158=-40

- 17+28-(35+2)=- 17+28-35-2=-( 17+35+2-28)=-26

-(- 12+8)-(26-8)= 12-8-26=8=- 14

1. Divide 100 into two parts, so that the first number plus 3 equals the second number minus 3. What are these two numbers?

Xiaoming and Xiaogang go to play by bike. They decided to start at 8 a.m. ahead of schedule. They expect to ride 7.5 kilometers per hour and arrive at 10 in the morning. Before they leave, they decide to arrive at their destination at 9 am. So, how many kilometers per hour?

Grandpa and grandson play chess. Grandpa won a set and grandson won three points. After eight innings, they scored even. How many sets did they win?

4. You need to print a document. It takes 6 o'clock for Xiao Li to do it alone and 8 o'clock for Xiao Wang to do it alone. If they do it together, how long will it take?

5. A harvester harvests wheat fields, 25% in the morning and 20% in the afternoon. As a result, there are still 6 hectares of wheat fields that have not been harvested. How many hectares is this wheat field?

6. A store sells two clothes, each 60 yuan. One of them earned 25% and the other lost 25%. Is this store profitable or losing money?

7.A train travels from A to B at a speed of 60 km/h, and B train travels from B to A at a speed of 90 km/h. It is known that A and B are 200 km apart. How far is it from A where the two cars meet?

8. It is known that points C and D are any two points on the line segment AB, AB = 20, CD = 8m, and N and P are the midpoint of AC, CD and BD respectively. Find am+Pb

9 、( 9/5X+X)+(4-X)=9/5(4-X)

10. It is known that the common ratio of line segment ab to cd is BD = 3 1ab = 4 1cd, and the distance between line segment AB and the midpoint E\F of CD is 10cm. Find the length of AB and CD

1 1. It is known that the line segment ab extends to C as BC = 2ab, the midpoint of AB is D, E and F are points on BC, be: EF = 1: 2, EF: FC = 2: 5, AC = 60 cm to find the length of DE and D F..

12. It is known that point M is the midpoint of line segment AB, AB = 28 cm, and point N is on line segment AB, an: Nb = 3 1: 15 \ 2. Find the length of MN.

Answer: 1, 53,47.

2.7.5× 2 =15km

15 ÷1=15km/h

Grandpa won six games of chess. Sun Tzu won two games of chess.

4.1÷ (1/6+1/8) = 24/7 hours

5,6 ÷ (1-25%-20%) =120/1hectare.

6.60× 2-60 ÷ (1+0.25)-60 ÷ (1-0.25) =-8 without 8 yuan.

7200(60+90)= 4/3 hours

60× 4/3 = 80km

8. Because M, N and P are the midpoint of AC, CD and BD respectively, AM = CM and Pb = PD.

So there are (am+Pb) x2+CD = AB = 20, (am+Pb) x2+8 = 20, and am+Pb = 6.

9.5/9x+x+4-x = 20/9-5/9x

10/9x=- 16/9

x=-8/5

10，AB=3BD，CD=4BD

EF: 1/2(a b+CD)-BD = 10

1/2(3BD+4BD)-BD= 10

2.5BD= 10

Bd = 4cm

AB=3BD= 12 CD=4BD= 16

1 1, because BC = 2ab and AC=60cm.

So BC+AB=60 and 2AB+AB=60, we can get AB=20 and BC=40.

Because be: ef = 1: 2, ef: fc = 2: 5,

So BE:EF:FC= 1:2:5, according to BC=40cm, we can get be = 40x 1/8 = 5cm, ef = 40x2/8 = 10cm.

DE = BD+BE = 1/2AB+BE = 10+5 = 15cm

DF = DE+EF = 15+ 10 = 25cm

12，AN:BN= 1/3:2/ 15=5:2

MN = BM-BN = 1/2AB-2/7AB = 3/ 14AB = 3/ 14x 28 = 6cm