19,20,21

19) An earthquake off the coast of Japan had a magnitude of 8.0 and it caused a tsunami. To the nearest tenth, determine the magnitude of an earthquake that is one-half as intense as this earthquake. Answer to the nearest tenth. 20) Imani invests $4,942 in a retirement account with a fixed annual interest rate of 2% compounded 2 times per year. How long will it take for the account balance to reach $6,931.54? 21) A cup of coffee contains 160 mg of caffeine. In a healthy adult, the mass, m grams, that remains after t hours is modelled by the function m = 160- To the nearest half hour, how long will it take until only 20 mg of caffeine remain