! A box contains a radioactive substance. The number of kilograms, r(t), at time t years
is given by r(t) = 2-0.002588t. How many kilograms will be remaining after 160 years?
1) about half of the original amount
2) about one-fourth of the original amount
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3) about one-eighth of the original amount
4) about three-fourths of the original amounT