Question

A person can row downstream 20km in 2hoursand upstream 4km is 2hours.find the man’s speed of

rowing in still water and the speed of the current.

Answer 1

let speed in still water = x km/hr
let speed of the current = y km/hr

speed for downstream = x+y
speed for upstream = x-y

for downstream
speed = distance÷time
x+y = 20÷2
x+y = 10 (1)

for upstream
speed = distance ÷time
x-y = 4÷2
x-y = 2 (2)

by using elimination method
add both equation

x+y = 10
x-y = 2

2x = 12
x = 12 ÷2
x = 6

put value of x in equation 2
x-y = 2
6-y = 2
-y = 2-6
-y = -4
y = 4

therefore, speed in still water = 6km/hr
speed of the current = 4 km/hr