The half-life of a substance is 120 days. The initial quantity is 72g.
a. Write the specific equation in the form A=Aoekt
b. How much will be left after 85 days?
c. How long until only 8 g is left?
A=A0e-kt. 1/2 A0= A0e-kτ Where τ is a half-life period. So we get K=ln(2)/ τ We have A=A0e- ln(2)t/ τ = 72e- ln(2)t/120. b. A= 72e- ln(2)85/120 = 44.17 g. c. 8= 72e- ln(2)t/120 -> 1/9=72e- ln(2)t/120 -> -2ln(3)= - ln(2)t/120 240 ln(3)/ln(2) = 379 days.