Question

A man can row 10.2 km downstream in 18 minutes. If the speed of the stream is 3.5 kmph, how much time he would take to cover 121.5 km upstream? (in hours)

Answer 1

Downstream:

v(boat/ bank)= v(boat/ stream)+v( stream/bank) = s/t

<=> v( boat/stream) +3.5= 10.2/(18/60) => v(boat/stream)=30.5kmph

Upstream:

v(boat/bank) = v( boat/stream) - v( stream/bank) =30.5 - 3.5 =27 kmph

t' = s' / v(boat/bank) = 121.5/27 =4.5 hrs