1, an enemy plane violated our airspace, and our plane immediately took off to meet it. When the two planes were 50 kilometers apart, the enemy plane twisted its nose and fled at a speed of 15 kilometers per minute, and our plane pursued at a speed of 22 kilometers per minute. When our plane chased it to a distance of 1 km, it fought fiercely with the enemy plane and shot it down half a minute later. How many minutes did it take for the enemy plane to escape and be annihilated by our plane?

Solution: the time of chasing the enemy plane = (50-1)/(22-15) = 49/7 = 7 minutes.

A * * * took 7+ 1/2=7.5 minutes.

2. Party A is in City A, and Party B and Party C are in City B at the same time. A travels 6 kilometers per hour, B travels 4.8 kilometers per hour and C travels 4.5 kilometers per hour. It is known that after A and B meet, A and C meet again after 1.2 hours. Find the distance between a and b.

Solution: the distance difference between B and C = (6+4.5) ×1.2 =12.6 km.

Meeting time of Party A and Party B = 12.6/(4.8-4.5)=42 hours.

Then AB distance = (6+4.8) × 42 = 453.6km.

3. Two cars, A and B, leave relatively from two places at the same time. The whole journey of A takes 10 hour, and the whole journey of B takes 15 hour. When they met, A traveled120km more than B. Find the distance between the two places.

Solution: speed ratio of Party A and Party B = distance ratio = inverse time ratio = 15: 10 = 3: 2.

When meeting, Party A walked 3/5 of the whole journey and Party B walked 2/5 of the whole journey.

So the distance = 120/(3/5-2/5)=600 kilometers.

4. The cruise ship goes downstream, not 7 kilometers per hour, but 5 kilometers per hour upstream. Two cruise ships set off from the same place at the same time, one of which went down the river and then returned; The other ship went upstream and returned. As a result, after 1 hour, they returned to the starting point at the same time, asking how long the two ships had traveled in the same direction during this 1 hour.

Solution: For a ship that goes downstream first and then upstream, downstream speed: upstream speed = 7: 5 = inverse ratio of time (because the round-trip distance is the same).

So his downstream time is 5/ 12 hours, and his upstream time is 7/ 12 hours.

For ships that go upstream first and then downstream, the upstream time is 7/ 12 hours and the downstream time is 5/ 12 hours.

Then the time in the same direction is 7/12-5/12 =1/6 hours.

The time for a ship to sail 46 kilometers downstream and 34 kilometers upstream is exactly equal to the time for it to sail 80 kilometers in still water. Given the current speed of 2 km/h, find the speed of the ship sailing in still water.

Solution: Let the still water velocity be km/h..

46/(a+2)+34/(a-2)=80/a

(80a-24)/((a+2)(a-2)]=80/a

24a= 160

A=20/3 km/h