Hospitals use the radioactive substance iodine-131 in research. It is effective in locating brain tumors and in measuring heart, liver, and thyroid activity. A hospital purchased 20 grams of the...

Hospitals use the radioactive substance iodine-131 in research. It is effective in locating brain tumors and in measuring heart, liver, and thyroid activity. A hospital purchased 20 grams of the substance. Eight days later, when a doctor wanted to use some of the iodine-131, he observed that only 10 grams remained (the rest had decayed).


Using the model

 based on the information above, predict how much iodine-131 will remain after four weeks. (Lett be measured in days. Round your answer to one decimal place.)