Question

A professional rower can paddle 320 miles upstream in 10 hours and downstream 320 miles in 5 hours. How fast is the current?

Answer 1

speed=distance/time
upstream speed=v-c
downstream speed= v+c
Upstream data:
d=320, t=10 h
speed=320/10=32
Downstream data: d=320 miles, t=5h
speed=320/5
=64 mph
With the above we get the following equations:
v-c=32
v+c=64
solving the above simultaneous equation we get:
2v=96
v=96/2
v=48 mph
c=48-32=16 mph
thus the speed of the current is 16 mph

Answer 2

Let r be the rower, and c be the current. Then:
320/r-c=10
320/r+c=5
10r-10c=320
5r+5c=320
Then
10r+10c=640
20r=960
r=48
c=16

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