Question

If a boat goes 7 Km upstream in 4 minutes and the speed of the stream is 3 Km per hour, then the speed of the boat in still water is:​

Answer 1

$\large\underline{\bf{Solution-}}$

Let speed of the boat in still water = 'x' km per hour

Speed of the stream = 3 km per hour.

We know,

• Speed of upstream = Speed of boat in still water- Speed of stream

It means,

• Speed of upstream = x - 3 km per hour.

Now,

According to statement,

• Distance covered in upstream = 7 km

• Speed of upstream = (x - 3) km per hour

• Time = 4 minutes

Now,

We know,

$\red{ \boxed{ \sf \: Distance = Speed \times Time}}$

Thus,

$\rm :\longmapsto\:7 = (x - 3) \times \dfrac{4}{60}$

$\rm :\longmapsto\:7 = (x - 3) \times \dfrac{1}{15}$

$\rm :\longmapsto\:15 \times 7 = x - 3$

$\rm :\longmapsto\:105 = x - 3$

$\bf\implies \:x = 108 \: km \: per \: hour$

Hence,

• Speed of boat in still water = 108 km/ hour

Additional Information :-

If speed of boat in still water is 'x' km per hour and speed of stream is 'y' km per hour, then

• Speed of downstream = Speed of boat in still water + Speed of stream

It means,

• Speed of downstream = ( x + y ) km per hour