Question 754313
A boat can travel at a speed of 12 km/h in still water. If it takes three hours to go
15 km upstream and back, find the speed of the current, giving your answer
correct to 2 decimal places.
***
let x=speed of current
12+x =speed of boat downstream
12-x =speed of boat upstream
travel time=distance/speed
..
{{{15/(12+x)+15/(12-x)=3}}}
LCD: (12+x)(12-x)
{{{15(12-x)+15(12+x)=3(144-x^2)}}}
180-15x+180+15x=432-3x^2
3x^2-72=0
x^2-24=0
x^2=24
x=-√24 (reject, x>0)
or
x=√24≈4.90
speed of current≈4.90 km/h