Answer:
30 grams
Step-by-step explanation:
half life is 60 days so every 60 days the amount 480 grams will be half
in 240 days will decay 240 /60 = 4 times
once 480 /2 = 240
twice 240 /2 = 120
trice 120 / 2 = 60
four times 60/2 = 30 grams will be left
