Question 316631
If a boat travels downstream for one hour and travels twelve miles and returns
 upstream to the starting point and the trip requires four hours how fast is the current
:
Let s = speed of boat in still water
Let c = speed of the current
:
Write a distance equation for each trip:
1(s + c) = 12
4(s - c) = 12
:
Simplify the second equation; divide by 4, subtract from the 1st equation
s + c =12
s - c = 3
-----------subtraction eliminates s, find c
 2c = 9
c = {{{9/2}}}
c = 4.5 mph is the current
:
:
:
Check solution, find the speed of the boat
s + 4.5 = 12
s = 12 - 4.5
s = 7.5 mph speed of the boat
Check solution in the return equation
4(7.5 - 4.5) = 
4(3) = 12