Question

Johnny and his father go fishing at 5:00 AM. After motoring 6 km upstream, Johnny writes a letter to his friend, puts the letter in a bottle and drops it into the river. the bottle floats in the current and reaches at 7 : 40 AM the point where Johnny and his father began the trip. If the speed of the boat in still water is 9 km/h, what is the speed of the river current?

Answer 1

Answer:

4.5

Step-by-step explanation:

Probably too late for your RSM homework, but here is the solution:

6/(9-x) [Time they motored upstream] +6/x [Time it took the bottle to get back to the starting point] = 8/3 [Total Time]

Simplify to 54/(x(9-x))=8/3

Cross multiply: 162=(8x)(9-x)

Simplify -x^2+9x=20.25

Multiply both sides by negative one and move 20.25 to the other side. x^2-9x+20.25=0

Solve and get 4.5 :D!