SOLUTION: In 8 hours, two campers rowed 15 miles down a river and then rowed back to their campsite. The rate of the river's current was 1 mph. Find the rate at which the campers row in calm

Question 304035: In 8 hours, two campers rowed 15 miles down a river and then rowed back to their campsite. The rate of the river's current was 1 mph. Find the rate at which the campers row in calm water.
What I know is that it was 8 hours total and it took 15 mi there and back.
Please help! I've been trying to solve it for now an hour and 31 minutes.
Answer by mananth(16946) (Show Source): You can put this solution on YOUR website!
let the speed of the boat be xmph in still water
down stream the speed will be x+1 mph
time taken down stream = 15 / x+1 hours
upstream the speed will be x-1 mph
time taken upstream = 15 / x-1
sum of these two times = 8 hours
15 / x+1 + 15 /x-1 = 8
15(x-1)+15(x+1) / x^2-1= 8
15x-15 +15x +15 = 8(x^2-1)
30x = 8x^2-8
8x^2-30x-8 =0
8x^2-32x+2x-8=0
8x(x-4)+2(x-4)=0
(x-4)(8x+2)=0
x= 4 or -2/8
the rowing speed in still waters = 4 mph
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