By the definition of half life, after 140 days the mass of the radioactive substance is half that at time 0.
ie.
The half life of Polonium-210 is 140 day and a sample of this element has a mass of 300 mg
Find the mass that remains after t days
y= f(t)
initial amount is 300 mg
f(t)= 300e^kt
To determine the value of k we use the fact that half life is 140d and so
f(140)= 150 thus
300e^140k=150
I am confused on how they get f(140) = 150?
since f(140)=300e^140k=/= 150??