10X= 15(X-30)
10X= 15X-450
-5X=-450
X=90 (minutes)
A: It takes 90 minutes to climb the mountain.
2. It takes 3 hours to sail upstream, 2 hours to sail downstream, and the speed of the ship in still water is calculated at a speed of 3 km/h.. Solution: let the speed of the ship in still water be x km/h.
2(X+3)=3(X-3)
2X+6=3X-9
-X=- 15
X= 15 (km/h)
A: The speed of the ship in still water is15km/h..
It takes 20 seconds for a train to pass through a 300-meter-long tunnel at a constant speed. There is a lamp at the top of the tunnel, which shines vertically downward. The time when the lamp shines on the train is 10 second. Find the length of the train.
Solution: Let the length of the train be x meters.
300+X/20=X/ 10
3000+ 10X=20X
- 10X=-3000
X=300 meters
Attendant: The length of this train is 300 meters.
4. The following are two charging methods for mobile phones: 1. The monthly fee is 30 yuan/month, and the call to 0.3 yuan/minute; 2. Call 0.4 yuan/min without paying the monthly fee. How long does a user talk? Do the two charging methods charge the same?
Solution: Let a user dial X points, and the two charging methods charge the same amount.
0.3X+30=0.4X
0.3X-0.4X=-30
-0. 1X=-30
X=300 (minutes)
Answer: The user calls for 300 minutes, and the two charging methods charge the same.
5. The distance between Party A and Party B from AB is 180km. Party A was riding a bicycle at a speed of 15km/h, and Party B was driving a car at a speed of 5km/h. How long did it take them to meet? Solution: Suppose two people meet after X hours.
15X+45X= 180
60X= 180
X=3 (hours)
A: Three hours later, the two met.
6. There were 68 original workers in Team A and 44 original workers in Team B, and 42 workers were transferred from these two teams. How many workers should be transferred to team A in order to make the number of team B reach 3/4 of that of team A?
Solution: suppose to transfer to team a with x people and team b with 42-x people.
3/4(68+x)=44+(42-x)
5 1+3/4X=86-X
7/4X=35
X=20 (person)
Answer: there should be 20 people transferred to team a.
7. Two sticks stand upright at the bottom of the barrel. After adding water into the barrel, the length of one stick exposed to the water is 1/3, and the length of the other stick exposed to the water is 1/5. Given that the sum of the lengths of two wooden sticks is 55 cm, calculate the water depth.
Solution: Let a stick be x cm long.
( 1- 1/3)X =( 1- 1/5)(55-X)
2/3 times =4/5(55 times)
22/ 15X=44
X=30 cm
(1- 1/3)X=20 (cm)
A: The water depth is 20 cm.
8. A two-digit number, in which the number of one digit is 2 larger than the number of the tenth digit, and the sum of the number of one digit and the number of the tenth digit is 10. Find this two-digit number. Solution: let the tenth digit be x.
X+(X+2)= 10
2X=8
X=4
(X+2)=6
A: This two-digit number is 46.
9. A job is completed by Party A alone for 20 hours and Party B alone 12 hours. If you do it for four hours first, how many hours will it take for the remaining two people to cooperate? Solution: It takes x hours to complete the installation.
1-4/20 =( 1/20+ 1/ 12)X
4/5 =2/ 15X
X =6 (hours)
A: It takes 6 hours to complete.
10. For a knowledge contest, give 50 questions, get 3 points for answering one question correctly, deduct 1 point for not answering or answering wrong, and get 142 points at the end of a class. How many questions do you want a class to answer correctly? Solution: Ask a class to answer X questions correctly.
3X- 1 (50-X)= 142
3X+X= 142+5
4X= 192
X=48 (topic)
A: One class answered 48 questions correctly.