The decaying rate of radium is directly proportional to its access mass.

a) Write a differential equation to relate mass of radium, x and time t.

b) If it takes 1400 years for a sample to lose half of its initial mass, how long does it take to lose 1% of the initial mass?

For question a) x=A(e^-kt) A=e^c

For question b) My problem was the initial mass...actually how to do this type of question??(IF mass was not given)