SOLUTION: A solution has a concentration of 10 milligrams of salt per cubic centimetre. Water is slowly added such that the concentration of salt is reduced by 20% every two hours. Determine

Question 122467: A solution has a concentration of 10 milligrams of salt per cubic centimetre. Water is slowly added such that the concentration of salt is reduced by 20% every two hours. Determine the equation that models the concentration of salt in terms of time and use it to find the concentration after 7 hours.
Answer by ankor@dixie-net.com(22740) (Show Source): You can put this solution on YOUR website!
A solution has a concentration of 10 milligrams of salt per cubic centimetre. Water is slowly added such that the concentration of salt is reduced by 20% every two hours. Determine the equation that models the concentration of salt in terms of time and use it to find the concentration after 7 hours.
:
Let t = time in hours
Let A = resulting amt
:
A 20% reduction leaves 80% changed to decimal .8
Use the exponent t/2 because it's every two hours
:
A = 10 * .8^(t/2)
:
In 7 hrs:
A = 10 * .8^(7/2)
A = 10 * .4579; (find .8^3.5 on a calc)
A = 4.579 milligrams after 7 hrs
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