To the nearest thousandth of a gram, how many grams of the substance remain in 1990?

Question

The rate of decay of a radioactive substance is proportional to the amount of substance present at any time t. In

1840 there were 50 grams of the substance and in 1910 there were 35 grams. To the nearest thousandth of a

gram, how many grams of the substance remain in 1990?

Answer 1

35 = 50e^70k

0.7 = e^70k

ln 0.7 = 70k

Determine the value of k, then substitute into

a = 35e^80k