Find the speed of Ferdinand in still water

Question

Ferdinand can swim 10 m downriver at the same time, he can swim 6 m upriver. The speed of the current is 4 m per hour. Find the speed of Ferdinand in still water. Let x be the speed of Ferdinand in still water. Let c be the speed of the current (4m/hour)

Answer 1

distance = rate if speed times time

d= rt

t = d/r

t = 10/(r+c) = 6/(r-c) where r= speed in still water

c=4 = river's current speed

10/(r+4) = 6/(r-4)

solve the equation for r

cross mulitiply

10r -40 = 6r +24

4r = 64

r = 64/4 = 16 mph = speed in still water

16+4 = 20. d/r = 10/20 = 1/2 hour down river

16-4 =12. dr/r = 6/12 = 1/2 hour upstream

1/2 hour upstream and 1/2 hour down stream.