SOLUTION: A boat travels 12 miles up the Mississippi River and 12 miles back down river in a total of eight hours. The rate of the boat in still water is four miles per hour. Find the speed

Question 347407: A boat travels 12 miles up the Mississippi River and 12 miles back down river in a total of eight hours. The rate of the boat in still water is four miles per hour. Find the speed of the current.
Found 2 solutions by mananth, josmiceli:
Answer by mananth(16946) (Show Source): You can put this solution on YOUR website!
let speed of current be xmph
downstream speed = x+4 mph
upstream speed = 4-x mph
Time downstream = 12/(x+4)
Time upstream = 12/(4-x)
....
12/(x+4)+12/(4-x)=8
LCD = (x+4)(4-x)
12(4-x)+12(x+4)/(x+4)(4-x)=8
-12x+48+12x+48 = 8(16-x^2)
96=128 8x^2
8x^2=128-96
8x^2=32
x^2=4
x= 2 mph the current speed.
Answer by josmiceli(19441) (Show Source): You can put this solution on YOUR website!
given:
mi/hr
mi
hrs
Going upstream:

Going downstream:

By substitution:

The speed of the current is 2 mi/hr
check answer:
Going upstream:

hrs
Going downstream:

hrs
hrs total
OK

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