2. The distance between a and B is 450 km. A car drives from a to B at three speeds: 50 km / h and 55 km / h 88 km / h, 7.2 hours in total. It is known that the car has driven for 2.4 hours at the speed of 50 km / h, how many hours has it driven at the speed of 88 km / h?

2. The distance between a and B is 450 km. A car drives from a to B at three speeds: 50 km / h and 55 km / h 88 km / h, 7.2 hours in total. It is known that the car has driven for 2.4 hours at the speed of 50 km / h, how many hours has it driven at the speed of 88 km / h?

55 km / h and 88 km / h
It took 7.2-2.4 = 4.8 hours
450-50x2.4 = 330km
Driving at 88km / h for (330-55x4.8) / (88-55) = 2 hours
A: I drove for 2 hours at the speed of 88 km / h
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The distance between a and B is 390 km. A car drives from a to B with a speed of 55 km per hour. After driving for 4 hours, it is required that the car must arrive at B within 2 hours. How much faster is the average speed of the car per hour?

390 divided by (4 + 2) = 65 km / h
65-55 = 10 km / h
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The distance between a and B is 180 kilometers. One person rides a bicycle from place a to place B, and his speed is 15 kilometers per hour. The other person rides a motorcycle from place B to place a, and turns back to place B immediately after arriving at place A. It is known that the speed of a motorcycle is three times of that of a bicycle, How long does it take for a motorcyclist to catch up with a cyclist

Motorcycle speed = 15 * 3 = 45 km / h
Let the motorcyclist catch up with the cyclist in X hours
45X-180=15X+15*2
The solution is x = 7 hours
So, after seven hours, motorcyclists catch up with cyclists

The distance between a and B is 90 kilometers. It took Uncle Wang 2 hours to go from a to B by motorcycle and 1.6 hours to return. What's the average speed of Uncle Wang's round trip

Total distance divided by total time equals average speed
90*2/（2+1.6）=50KM/H