Question 304035
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