Approximately days have passed when 20% of cobalt (co) remains?

The half-life of Cobalt 60 is 5.27 years. This means that after this time, only 50 % of the initial amount of Cobalt is left. The relationship between the number of nuclei left at time t and the time, for a radioactive decay, is given by

where  is the number of nuclei left at time t,  is the number of nuclei at t=0, and  is the half-life. For cobalt, .

We can re-arrange the formula as

and then

the problem asks for the time t at which only 20% of cobalt is left, that means the time t at which

therefore, using this into the previous equation, we get

so, after a time of 12.24 years, only 20% of cobalt is left.

Iread this book last year so take this with a grain of salt.gene jumps from the tree to compete with finny due to the fact that gene is always trying to do better than finny. he is put under the grasp of peer pressure due to finny almost forcing him to do this. ever since he first jumped finny kept pressuring him to jump since he thought gene enjoyed jumping.rather than uses this answer you should probably just reread chapters 3-4