Question

The speed of a boat in still water in 8 km/h. and the speed of the stream is 2.5 km/h. Find the time taken by the boat to go 63 km downstream.​

Answer 1

Step-by-step explanation:

Let x be the speed of the stream.

⇒  Speed of the boat in still water is 8km/hr

⇒  The speed of the boat in upstream is 8−xkm/hr

⇒  The speed of the boat in downstream is 8+xkm/hr

⇒  The time taken by the boat to cover 15km=8−x15hr

⇒  The time taken by the boat to cover 22km=8+x22hr

According to the question,

⇒  8−x15+8+x22=5

⇒  15(8+x)+22(8−x)=5(8−x)(8+x)

⇒  120+15x+176−22x=5(64−x2)

⇒  296−7x=320−5x2

⇒  5x2−7x−24=0

⇒  5x2−15x+8x−24=0

⇒  5x(x−3)+8(x−3)=0

⇒  (x−3)(5x+8)=0

⇒  x−3=0 and