The average speed of car uphill is a kilometer per hour, and the average speed of car downhill is B kilometer per hour. The distance of car uphill and downhill is s kilometer 1. How many hours does it take for the car to go up and down the mountain at a time 2. What is the average speed of the car up and down the hill 3. If a = 40 km / h, B = 60 km / h, s = 120 km, then how many hours does it take for the car to go up and down the mountain at a time? What is the average speed of the car up and down the mountain

The average speed of car uphill is a kilometer per hour, and the average speed of car downhill is B kilometer per hour. The distance of car uphill and downhill is s kilometer 1. How many hours does it take for the car to go up and down the mountain at a time 2. What is the average speed of the car up and down the hill 3. If a = 40 km / h, B = 60 km / h, s = 120 km, then how many hours does it take for the car to go up and down the mountain at a time? What is the average speed of the car up and down the mountain

(1)(s/a)+(s/b)
(2)2s/[(s/a)+(s/b)]
(3) Bring the condition into (1) (2)

When a car goes up the mountain, it's 30 kilometers per hour. It takes 4 hours to reach the top of the mountain. When it goes down the mountain, it's back on the same road. It's 60 kilometers per hour. What's the average speed up and down the mountain

2 ÷ (1 / 30 + 1 / 60) = 40 km / h
So the average speed up and down the mountain is 40 km / h

A car drove from a to B, 40 kilometers per hour. Five hours later, a train drove from a to B at the speed of 90 kilometers per hour, and caught up with the car at the midpoint between a and B______ Kilometers

A: the distance between the two places is 720 km