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Helpful source:
https://percent-calc.com/what-is-9-of-15000
9,500 just add the 0 always add 0 if you multiply by 10. 00 for 100 and 000 for 1000
Answer:
a)
, b)
, c)
, d) 
Step-by-step explanation:
a) Let assume an initial mass m decaying at a constant rate k throughout time, the differential equation is:

b) The general solution is found after separating variables and integrating each sides:

Where
is the time constant and 
c) The time constant is:


The particular solution of the differential equation is:

d) The amount of radium after 300 years is:
