Question 913460
r*t=d
IF three hours is the total time then u+d=3

20u=16d
5u=4d
u+d=3
u=3-d
5*(3-d)=4d
15-5d=4d
15=9d
5=3d
5/3=d 1 2/3
u=9/3-5/3=4/3 1 1/3

20*4/3=80/3=33 1/3 miles  upstream in 1:20
16*5/3=80/3=33 1/3 miles downstream in 1:40