A girl rows 11 km downstream in 2 h. Her return trip takes 4 h. How fast is the current. in km/h?

Answer 1

What is phisecs, some small unit of time?

rowing rate --- x km/h
current rate --- y km/h

A girl rows 11 km downstream in 2 h
---> 2(x+y) = 11
2x + 2y = 11

"Her return trip takes 4 h"
---> 4(x-y) = 11
4x - 4y = 11

first times 2
4x + 4y = 22
add to the 2nd

8x = 33
x = 33/8 km/h
y = (11 - 2(33/8)/2 = 11/8

the current speed is 11/8 km/h

check:
downstream:
2(33/8+11/8) = 2(5.5) = 11
upstream:
4(33/8 - 11/8) = 4(2.75) = 11
My answer is correct!

Answer 2

thank you so much !!!