Answer:
OUR ANSWER IS 4.46 WHICH IS APPROXIMATELY 4.5
Explanation:
check to see how much salt is coming in and going out. Since pure water contains no salt, and the 5 gallons leaving contain 5/100 of the salt present, we have
ds/dt = 5/100 * 0 - 5/100 s
ds/dt = -1/20 s
ds/s = -1/20 dt
s = c*e^(-t/20)
Since s(0) = 10,
s = 10*e^-(t/20)
so, let's find t when s=8
10 e^(-t/20) = 8
e^(-t/20) = 0.8
-t/20 = ln0.8
t = -20 ln0.8 = 4.46
=4.5
