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 =
time downstream =
the ferry trip upstream takes twice as long as its return trip downstream
=
divide both sides by d
=
cross multiply
Add 2x on both sideds
subtract 15 from both sides and divide by 3
x=5
Speed of river's current = 5 mph