How long does it take for 10.0 g of a radioactive isotope to decay to 1.25 g if its half-life is 17.0 d?

Answer 1

k = 0.693/t_1/2
Then substitute k into the below.

ln(No/N) = kt
No = 10g
N = 1.25
k from above
Solve for k in days.