The speed of boat 'A' in upstream and still water is in the

Solution

Let the upstream speed and still water speed of boat 'A' be 3x km/hr and 5x km/hr.

So, the downstream speed of boat 'A' = (5x - 3x + 5x) = 7x km/hr

Speed of stream = (5x - 3x) = 2x km/hr

ATQ,

(175/7x) + (275/5x) = 16

So, (25/x) + (55/x) = 16

So, (80/x) = 16

So, 'x' = 5

So, still water speed of boat 'A' = 5 X 5 = 25 km/hr

Still water speed of boat 'B' = 25 X 0.8 = 20 km/hr

Increased speed of stream = 2 X 5 X 1.2 = 12 km/hr

So, required time = {480 ÷ (20 + 12) } + {360 ÷ (20 - 12)} = 15 + 45 = 60 hours