My only problem with this question is counting the number of days... Is it 15 or 16? And is my method for this question correct?

100 x 0.4 = 40 kg of Isotope A

100 x 0.6 = 60 kg of Isotope B

If we say the number of days between August 31st and September 15th is 15,

15/1 = 15

15/3 = 5

40 x 0.5

^{15}= 5/4096 kg

60 x 0.5

^{5}= 1.875 kg

1.2207... + 1875 = 1876 g