the half-life f a radioactive element is 149 day, but your sample will not be useful to you after 70% of the radioactive nuclei orignally present have disintegrated. about how many days can you use the sample? a. 224 bb. 259 c. 264 d. 269

Question

the half-life f a radioactive element is 149 day, but  your sample will not be useful to you after 70% of the radioactive nuclei orignally present have disintegrated. about how many days can you use the sample? a. 224 bb. 259 c. 264 d. 269

anonymous · Answer

pretty much identical to this one http://openstudy.com/users/danielle2012#/updates/4f71b5bfe4b07738f5ade82a

anonymous · Answer

$$(\frac{1}{2})^{\frac{t}{149}}=.3$$
$$\frac{t}{149}=\frac{\ln(.3)}{\ln(.5)}$$
$$t=\frac{149\ln(.3)}{\ln(.5)}$$