Suppose a laboratory has a 31 g sample of polonium-210. the half-life of polonium-210 is about 138 days. a. how many half-lives of polonium-210 occur in 966 days? b. how much polonium is in the sample 966 days later?

Po 210 T½ = 138 days
Half-Lives = 966 / 138 = 7 half lives
For EACH half life, one half of the original remains.
So, for 7 half lives, we would have 1 / (2^7) remaining.
2^7 = 128
1 / 128 = 0.0078125

So, after 966 days we would have:
31 * 0.0078125 = 0.2421875 grams remaining
Source1728.com/halflife.htm