Answer:
Speed of the river = [tex]\frac{4}{3}[/tex] km per hour
Step-by-step explanation:
Speed of the boat in still water = 4 km per hour
Let the speed of the river = v km per hour
Speed of the boat upstream = (4 - v) km per hour
Time taken to cover 6 km = [tex]\frac{\text{Distance}}{\text{Speed}}[/tex]
= [tex]\frac{6}{4-v}[/tex] hours
Speed of the boat downstream = (4 + v) km per hour
Time taken to cover 12 km = [tex]\frac{12}{4+v}[/tex] hours
Since, time taken by the boat in both the cases is same,
[tex]\frac{6}{4-v}= \frac{12}{4+v}[/tex]
6(4 + v) = 12(4 - v)
24 + 6v = 48 - 12v
12v + 6v = 48 - 24
18v = 24
v = [tex]\frac{24}{18}[/tex]
v = [tex]\frac{4}{3}[/tex] km per hour
