Question

There are 3.29g of Iodine 126 remaining in a smaple originally containing 26.3 g of iodine 126 the half life of iodine 126 is 13 days. How old is the sample?

Answer 1

k = 0.693/t_1/2.

Then ln(No/N) = kt
No = 26.3
N = 3.29
k from above.
solve for t.
Post your work if you get stuck.