AFCAT Model Paper 10

Given:
Speed of boat in still water = 6 km/hr
Speed of the river = 2 km/hr
Time difference between upstream and downstream for same distance = 2 hours
Concept used:
Upstream speed = Speed of boat – speed of the river
Downstream speed = Speed of boat + speed of river
For a given distance, speed ∝ (1/time)
Calculation:
Speed in upstream = 6 - 2 = 4km/ hr
Speed in downstream = 6 + 2 = 8km/ hr
Let the distance travelled be x km
Upstream time =(

x

4

) hr
Downstream time =(

x

8

) hr
So, (

x

4

)−(

x

8

)=2
⇒ 2x - x = 16
⇒ x = 16 km
∴ The distance travelled is 16 km.