Answer:
14mph
Explanation:
let speed in still water be represented as y
The speed of the stream is given as 3mph
distance traveled by boat upstream = 11 Miles
distance traveled by boat downstream = 17 miles
∴ speed when the boat travels upstream = y-3
speed when the boat travels downstream = y+3
speed = [tex]\frac{distance}{time}[/tex]
time = [tex]\frac{distance}{speed}[/tex]
time taken to go upstream = [tex]\frac{11}{y - 3}[/tex]
time taken to go downstream = [tex]\frac{17}{y + 3}[/tex]
assuming that time taken to travel upstream = time taken to travel downstream
[tex]\frac{11}{y - 3}[/tex] = [tex]\frac{17}{y + 3}[/tex]
by cross multiplication,
11(y+3)=17(y-3)
11y + 33 = 17y - 51
17y - 11y = 33 + 51
6y=84
y= 84/6
y=14
there the speed in still water is 14mph
