For the subject Becquerel(Bq) to disintegerate from 11.5Mbq to 4.6 MBq takes 8 hours. How much percent does it disintegerate per hours?And how big is it after a 24 hours if it starts from 11.5 MBq?

Final = Initial*e^rt

4.6 = 11.5e^8r

4.6/11.5 = 2/5 = e^8r

ln(2/5) = ln(2) - ln(5) = 8r

(ln(2) - ln(5))/8 = r ~ -11%/hour.

To find how much is left after 24 hours:

Final = 11.5e^{[24(ln(2)-ln(5))/8]} = 11.5e^{[3(ln(2)-ln(5))]} = 11.5(2/5)³