Question

a 25 gram sample of a substance that's used for drug research has a k-value of 0.1205 what is the substances half-life in days

Answer 1

y = y_0 * e^(kt)
where y = the final amount, y_0 = the initial amount, k is the decay constant, and t is the time

it's asking about half life so set y = (1/2)y_0. you will notice that y_0 cancels out on both sides of the equation. then plug in k. then solve for t.

Answer 2

or I guess you could just do ln(2)/k as it's been worked out in the example above