A boat can travel with a speed of 15 km/hr in still water. If the speed of the stream is 5 km/hr, find the time taken by the boat to go 200 km downstream.

Options
- 12 hrs
- 10 hrs
- 8 hrs
- 6 hrs

CORRECT ANSWER : 10 hrs

Discussion Board
Answer explanation

Speed of the still water = 1/2(a+b)
1/2(a+b)=15------> a+b=30 km/hr------------------path 1

Speed of the stream = 1/2(a-b)
1/2(a-b)=5--------> a-b=10 km/hr-------------------path 2

solve the equation
-------------------
a+b = 30
a-b = 10

2a=40 (speed downstream) a=20 km/hr, (speed upstream)b=10km/hr


Distance = speed * time (200km downstream , so take the speed of downstream)
200 km =20 km/hr*x
x=200/20
x=10 hrs



Shalini 05-5-2020 03:23 AM

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