When a drug is administered intravenously, the concentration of the drug begins to decrease immediately administered. One model for the blood concentration C, in milligrams per liter, after t hours is : C = 10e^-t - 2e^-2t. During what time period is the drug concentration level at least 0.88 milligrams per litre?

Coral reefs throughout the world are dying at a continuous rate of about 1.5% per year. Write an equation that can be used to determine the future area of a reef that now has an area of 150 km^2. Let c be the area of the coral reef t years from now. The equation is:    The equation is in the      family Use the equation to determine how many years until the reef decays to an area of 99 km^2? Round to the nearest year.

The number N of E.Coli bacteria in the millions per mililiter after t minutes can be modeled by N (t)=0.5^e0.014t. Determine the elapsed time required for the concentration of bacteria to reach 25 million per mililiter.

Four hundred grams of a radioactive material decays according to the formula A = 400(2/3)^t, where t is measured in years. Find the amount present in 10 years. Round to the nearest one-tenth of a gram.