A man can row 5 km/h in still water. If the speed of the current is 2.5 km/h, it takes 4 hours more in upstream than downstream for the same distance. The distance is:
Show answer & explanation
Correct answer: B
Explanation
The correct answer is option 2 i.e. 15km
Distance = speed × time
Let he takes 't' hours to cover the distance in downstream
Speed of downstream = B + S
Speed of upstream = B - S
Where B = speed of boat in still water
S = speed of current
As the distance travelled is same in both cases ,
t × (B + S ) = (t + 4) × (B - S)
t × (5 + 2.5 ) = (t + 4) × (5 - 2.5)
t × 7.5 = (t + 4) × 2.5
5t = 10
t = 2
Distance = 2 × (5 + 2.5 )
= 2 × 7.5 = 15