A boat takes 4hours for traveling downstream from point P to point Q and coming back to point P upst...........

Explanation:

Explanation:
Time taken by boat to travel upstream and downstream = 4 hours
Velocity of the stream, ½ (a-b) = 2km/hr
a-b = 4km/hr ……………….( 1)
velocity of the boat in still water = ½ (a+b) = 4km/hr
a+b = 8 km/hr ………………(2)
1 +2 we get a = 6 km/hr ,b = 2km/hr
let the distance between A and B be x km
x / 2 + x / 6 = 4
3x + x / 6 = 4  4x = 24 so,x = 6
distance between P and Q = 6km