Please help. Preparing for an exam.

Problem 1. (1 point) Problem 3. (1 point) A bacteria culture starts with 640 bacteria and grows at a rate A 6-kg quantity of radioactive isotope decays to 5 kg after 3 years. proportional to its size. After 3 hours there will be 1920 bacteria. Find the decay constant of the isotope. (a) Express the population after : hours as a function of t. k =. population: (function of () Answer(s) submissed: (b) What will be the population after 9 hours? (incorrect) (c) How long will it take for the population to reach 2130 ? Answer(s) submitted: Problem 2. (1 point) (incorrect) Problem 4. (1 point) The decay constant of Fermium-100 is 2.47 inverse-years. What An unknown radioactive element decays into non-radioactive sub- is its half-life? stances. In 760 days the radioactivity of a sample decreases by 77 percent. Answer(s) submitred: (a) What is the half-life of the element? half-life: (days) (incorrect) (b) How long will it take for a sample of 100 mg to decay to 88 mg? time needed: (days) Answer(s) submitted: (incorrect)