Question

A man can row 7.5km/hr in still water and he takes 6.5 times as long as to row upstream as to row downstream.The speed of current is?

Answer 1

let the speed of the stream(s2)=x
s1(man)=7.5km/hr
speed upstream=7.5-x
speed downstream=7.5+x
let time taken to row upstream=6.5y  then,
 taken to row downstream=y
distance=speed*time
⇒(7.5+x)y=(7.5-x)6.5y
⇒(7.5+x)=(7.5-x)6.5        [y and y cancel out each other]
⇒(7.5+x) =48.75 - 6.5x
⇒7.5 x=42.25
⇒x=5.633

Answer 2

answer is 5.5
because 48.75 - 7.5 = 41.25
and on dividing
41.25/7.5 = 5.5