The seventh math book p 104? 6~7 answers? Soviet version

1 1. It is known that a railway bridge is 1000 meters long and a train passes by. It takes 1 minute for the train to get on the bridge from the start point to the end point, and the whole train will get on the bridge completely for 40 seconds. What about the speed and length of the train?

Let the train speed be one meter per second and the car body length be b meters.

1 min =60 seconds

60a= 1000+b

40a= 1000-b

100a=2000

A = 20m m/s

b=60x20- 1000

B=200 meters

It is 200 meters long. The vehicle speed is 20m/s.

12, Party A and Party B run on the circular road at a constant speed, if they start at the same time. Walk in opposite directions and meet every 2 minutes; If you go in the same direction, meet every 6 minutes. It is known that A runs faster than B. How many laps do A and B run per minute?

Solution: Let A run X laps per minute and B run Y laps per minute. According to the meaning of the question in the equation:

2X+2Y= 1

6X-6Y= 1

Find X= 1/3.

，Y= 1/6

A: A runs 1/3 laps per minute, and B runs 1/6 laps per minute.

13, RMB 100 includes fifty cents, one yuan and two yuan, totaling 100 yuan. The sum of 50 points of 2 yuan is 75 yuan. How much is each kind in RMB?

Solution: Suppose there are five-corner A cards, one-dollar B cards and two-dollar 100-a-b cards.

According to the meaning of the question

0.5a+b+ 2×( 100-a-b)= 100( 1)

0.5a+2×( 100-a-b)=75(2)

(2) Replace (1)