A car from a to B can arrive one hour earlier if the speed is increased by 20%. If the speed is increased by 25% after driving at the original speed of 120 km, it can arrive 401 minutes earlier. How many km is the difference between a and B?

A car from a to B can arrive one hour earlier if the speed is increased by 20%. If the speed is increased by 25% after driving at the original speed of 120 km, it can arrive 401 minutes earlier. How many km is the difference between a and B?

Speed ratio = 1: (1 + 20%) = 5:6
Time ratio (inversely proportional to speed ratio) = 6:5
Original planned time = 1 △ 5 / 6 = 6 (hours)
Speed ratio = 1: (1 + 25%) = 4:5
Time ratio = 5:4
40 minutes = 2 / 3 hours 1-4 / 5 = 1 / 5
2 / 3 △ 1 / 5 = 10 / 3 (hours)
6-10 / 3 = 8 / 3 (hours)
120 △ 8 / 3 × 6 = 270 (km)
A: the difference between a and B is 270 km

The distance between a and B is 380 km. A bus runs 42 km per hour from place a to place B. after 100 km, a truck runs 38 km per hour from place B to place A. how many hours after the truck leaves, does it meet the bus?

(380-100) / (42 + 38) = 3.5 hours
The first 100 km of the bus is removed, and the remaining 280 km is the meeting distance between the two cars. The meeting distance = speed and X meeting time
So encounter time = distance / speed and