Answer:
Distance between A and B is 5400 meters
Explanation:
Consider "D" the letter to identify distance between A and B
Let's use "t" to identify the time of the first encounter (Devi and Kumar), and create an equation that states that the distance covered by Devi (at 100 m/min) in time "t", is equal to the total distance D minus what Kumar has covered at his speed (80 m/min) in that same time:
Recall that distance equals the speed times the time:
distance= speed * time
First encounter:
100 * t = D - 80 * t
180 * t = D Equation (1)
Not, 6 minutes later (at time t+6) , Devi and Li Ting meet .
Then for this encounter the distance covered by Devi equals total distance d minus the distance covered by Li Ting:
100 *(t+6) = D - 75 * (t+6)
100 t + 600 = D - 75 t - 450
175 T + 150 = D Equation (2)
Now, let's equal equation (1) to equation (2), since D should be the same:
180 t = 175 t + 150
5 t = 150
t = 30
Then the time t (first encounter) is 30 minutes. Knowing this, we can use either equation to find D:
From Equation (1) for example: D = 180 * t = 180 * 30 = 5400 meters