So I need that in micrograms tho. So 4402*10^-18/1000=4.4*10^-18kg. or 4.4*10^-12 micrograms
that stills say it's wrong tho.
I agree, but when you start with the equation A = λ N, then you say A = 4*10^9Bq, that "A" is the final A and the number N = 9.56*10^17 that you get from it is the final N. So, what is the initial N that should be larger than 9.56*10^17? That's why I suggested that you find the initial activity in post #2.The Initial should be bigger.
I prefer to look at it this way: If you have N atoms of atomic weight AW, the mass of the sample is given byJust realized I may have had it right but I forgot to convert the kg to g. So my answer should have been 6.28ug