Question

A ferry departs from a port along the Sands River at 10:00 am. The ferry travels at a speed of 15 mph in still water and returns to port at 2:00 pm. If the ferry trip upstream takes twice as long as its return trip downstream, what is the speed of the river’s current

Answer 1

Answer:

Speed of river's current = 5 mph

Step-by-step explanation:

Let 'd' be the distance covered  

 Let x be the speed of the rivers current

Speed upstream = 15-x

speed downstream = 15+x

Time = distance / speed

time upstream = $\frac{d}{15-x}$

time downstream = $\frac{d}{15+x}$

the ferry trip upstream takes twice as long as its return trip downstream

$\frac{d}{15-x}$= $\frac{2d}{15+x}$

divide both sides by d

$\frac{1}{15-x}$= $\frac{2}{15+x}$

cross multiply

$15+x= 2(15-x)$

$15+x= 30-2x$

Add 2x on both sideds

$15+3x= 30$

subtract 15 from both sides and divide by 3

$3x=15$

x=5

Speed of river's current = 5 mph