chemistry
posted by Massiel .
The half live of Iodine131 is 8 days. if you started out with 40 mg sample of iodine131, then what would be the mass of the sample after 32 days? please show your work

32 days is 4 halflives. So, the mass is reduced to 1/2^4 = 1/16 of 40mg, or 2.5mg

Just to be picky I think this problem is not stated correctly (although who am I to know what the author was thinking when this problem was written?). However, I think the spirit of the question expects an answer that Steve gave. Let me point out though that the question asks for the mass of the SAMPLE and that is the mass of I131(2.5 mg) + the mass of the decay products whatever they may be.