(Material from Appendix II in the Text)

For Mary: Nm = N0e+1.0t

For Joan: Nj = N0e-2.0t

Find t for which Nm = 4Nj

or, N0e+1.0t = 4 N0e+2.0t

e+1.0t/e-2.0t = 4
take natural logs
3.0t = ln 4

t = (ln4)/3.0 days

Answer is E

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