Bob can row 9mph...

Question

Bob can row 9 mph in still water. The total time to travel downstream and return upstream to the starting point is 3 hours and 36 minutes. If the total distance downstream and back is 26 miles, determine the speed of the river (current speed).

Answer 1

current is 4 mph, boat is 9 mph

that's 4+9=13 mph downstream

and 9-4 = 5 mph upstream

1 hour downstream

2.6 hours upstream

13x1 + 5x2.6 = 13+13= 26 miles total

T

distance = speed times time

d= st

time = d/s

3 hours and 36 minutes = 3.6 hours

26 = (9+c)T + (9-c)(3.6-T)

13 = (9+c)T

13= (9-c)(3.6-T)

2 equations 2 unknowns

solve by substitution and elimination

c=4 mph= current speed, T= 1 hour = time downstream