Question

Please solve this problem???​

Answer 1

Solution :

As per the given data ,

Speed of the boat in still water = 6.5 km / hr

Speed of the stream = 15 km / hr

Speed of the water upstream = 15 - 6.5 = 8.5 km / hr

Speed of the water downstream = 15 + 6.5 = 21.5 km / hr

Let the distance traveled by the boat upstream = Distance traveled by the boat downstream = d

Total distance traveled by the boat = 2d

We know that ,

$\dag \boxed{ s = \dfrac{d}{t}}$

here ,

• s = speed
• d = distance
• t = time

Hence ,

$\leadsto t_1 = \dfrac{d}{8.5 }$

$\leadsto t_1 = \dfrac{d}{21.5 }$

Total time taken ,

$\leadsto t = \dfrac{d}{8.5 }+ \dfrac{d}{21.5 }$

We know that ,

$\leadsto Avg.speed = \dfrac{total\: distance }{total\: time }$

$\leadsto Avg.speed = \dfrac{2d }{ \dfrac{d}{8.5 }+ \dfrac{d}{21.5 }}$

$\leadsto Avg.speed = \dfrac{2 }{ \dfrac{1}{8.5 }+ \dfrac{1}{21.5 }}$

$\leadsto Avg.speed = \dfrac{2 }{ \dfrac{21.5 +8.5}{ 8.5 \times21.5 }}$

$\leadsto Avg.speed = \dfrac{2 }{ \dfrac{30}{ 182.75 }}$

$\leadsto Avg.speed = \dfrac{182.75 }{ 15}$

$\leadsto\boxed{ Avg.speed =12.18 \dfrac{km }{ hr}}$

The average speed of the boat in the entire journey is 12.18 km / hr

Answer 2

Solution :

As per the given data ,

Speed of the boat in still water = 6.5 km / hr

Speed of the stream = 15 km / hr

Speed of the water upstream = 15 - 6.5 = 8.5 km / hr

Speed of the water downstream = 15 + 6.5 = 21.5 km / hr

Let the distance traveled by the boat upstream = Distance traveled by the boat downstream = d

Total distance traveled by the boat = 2d

We know that ,

$\dag \boxed{ s = \dfrac{d}{t}}$

here ,

s = speed

d = distance

t = time

Hence ,

$\leadsto t_1 = \dfrac{d}{8.5 }$

$\leadsto t_1 = \dfrac{d}{21.5 }$

Total time taken ,

$\leadsto t = \dfrac{d}{8.5 }+ \dfrac{d}{21.5 }$

We know that ,

$\leadsto Avg.speed = \dfrac{total\: distance }{total\: time }$

$\leadsto Avg.speed = \dfrac{2d }{ \dfrac{d}{8.5 }+ \dfrac{d}{21.5 }}$

$\leadsto Avg.speed = \dfrac{2 }{ \dfrac{1}{8.5 }+ \dfrac{1}{21.5 }}$

$\leadsto Avg.speed = \dfrac{2 }{ \dfrac{21.5 +8.5}{ 8.5 \times21.5 }}$

$\leadsto Avg.speed = \dfrac{2 }{ \dfrac{30}{ 182.75 }}$

$\leadsto Avg.speed = \dfrac{182.75 }{ 15}$

$\leadsto\boxed{ Avg.speed =12.18 \dfrac{km }{ hr}}$

The average speed of the boat in the entire journey is 12.18 km / hr