3. During a period of 9 months, the number of people owning a flip-o-phone has increased from 285 000 to 315 000. Calculate how many months after the start of the 9-month-period we can expect 400 000 own- ers of a flip-o-phone if we assume that their number a. grows according to a linear function; b. grows exponentially; c. grows according to a formula of the form F(t) = 500 000 a ebt, where a and b are constants and where F denotes the number of owners of a flip-o-phone and t the time in months since the start of the 9-month-period.

A radiation safety officer is working with 112 grams of a radioactive substance. After 17 days, thesample has decayed to 80 grams. Rounding to fivesignificant digits, write an exponential equationrepresenting this situation. To the nearest day, whatis the half-life of this substance?

Use a graphing calculator to solve each problem. In Example 4, suppose that a birth control program changed the formula for poulation growth to Pt=1000e0.01t. How long will the food supply be adequate? EXAMPLE 4 Using a Graphing Calculator to Solve a popuiation Problem Suppose that a country with a population of 1000 people is growing exponentially according to the population function Pt=1000e0.02t Where t in years. Furthermore, assume that the food supply, measured in adequate food per day per person, is growing linearly according to the function fx=30.625x+2000 In how many years will the population outstrip the food supply?