A radioactive material, for example the isotope carbon-14, disintegrates at a rate proportional to the amount currently present. Let W(t) be the amount present at time t, measured in days, and r be the proportionality constant, the decay rate.
(a) Write a differential equation to describe the decay process.
(b) If 100 mg of carbon-14 decays to 82.04 mg in one week, determine the decay rate, r.
(c) Find an expression for the amount of carbon-14 present at any time, t.
(d) Find the time required for the thorium to decay to one-half its original amount.
i know that the de :
dW/dt = -k dt
and W(t) = A e-kt
but i dunno how to solve (b), (c) and (d)....
pls help me....