a sailor can row a boat 8km down stream and return back to the starting point in 1 hour 40 minutes . if the speed of the stream is 2km per hour,find the speed of the boat in still water
Answers
Answered by
1
Step-by-step explanation:
Speed of the stream =2 km/hr
Let speed of the boat in still water be x km/hr.
Time taken to travel downstream =
x+2
8
Time taken to travel upstream =
x−2
8
Total time =1 hr. 40 min =
3
5
hr.
Therefore,
x+2
8
+
x−2
8
=
3
5
⇒3(8x−16+8x+16)=5(x
2
−4)
⇒24x+24x=5x
2
−20
⇒5x
2
−48x−20=0
⇒5x
2
−50x+2x−20=0
⇒5x(x−10)+2(x−10)=0
⇒(x−10)(5x−2)=0
⇒x=10,
5
2
As speed cannot be in fraction, x=10 is the correct value.
Thus, speed of boat in still water is 10 km/hr.
Similar questions