Question

A boat has a speed of 9 mph in calm water. It takes the boat 4 hours to travel upstream but only 2 hours to travel the same distance downstream. Which equation can be used to find c, the speed of the current?

Answer 1

Answer: 4 ( 9 - c ) = 2 ( 9 + c )

Step-by-step explanation:

Since, Distance = Speed × Time

Here c represents the speed of current,

Thus, if the boat has the speed of 9 mph in still water,

Then its speed in upstream = ( 9 - c ) mph

Also, It takes the boat 4 hours to travel upstream.

Hence, total distance in upstream = 4 ( 9 - c )

Similarly its speed in downstream = ( 9 + c ) mph

Also, It takes the boat 2 hours to travel downstream.

Hence, total distance in downstream = 2 ( 9 + c )

Since, the distance in upstream and downstream is equal.

⇒ 4 ( 9 - c ) = 2 ( 9 + c )

Which is the required equation for finding the speed of current c..

Answer 2

D=4(9-c) and d=2(9+c)

d=36-4c and d=18+2c

Since d=d

18+2c=36-4c  add 4c to both sides

18+6c=36  subtract 18 from both sides

6c=18  divide both sides by 6

c=3

So the speed of the current is 3mph