Chemistry help??

Question

Can u please help me answer these questions?

http://img229.imageshack.us/img229/5973/scankn3.jpg

i just need the answer to number 26.

and question 27

Answer 1

Rn-222 --> He (alpha particle)+ Po-218

ln(2/1) = k x 3.82 day
k = 0.1815 day^-1
ln(1.0/x) = 0.1845 x 7.64 day
x = 0.25 g
easy way-
half life = 3.82 days
7.64/3.82 = 2 half lifes
1.0 --> 0.50 --> 0.25g

Answer 2

Rn-222 ===> Po-218 + He-4 (alpha particle)

7.64 = 2 x 3.82, so after 3.82 days, 0.5g would be left, and after 7.64 days, 0.25g would be left: Two half-lives having elapsed.