Chapter 12.6, Problem 83PE

Phosphorus $32\left(\text{P}\right)$ has a half-life of approximately 14 days. If 10 g of ${}^{32}\text{P}$ is present initially, then the amount $A\left(t\right)$ (in grams) of phosphorus 32 still present after t days is given by $A\left(t\right)=10{\left(0.5\right)}^{t/14}$. (See Example 11.)

a. Find the amount of phosphorus 32 still present after 5 days. Round to the nearest tenth of a gram.

b. Find the amount of time necessary for the amount of ${}^{\text{32}}\text{P}$ to decay to 4 g. Round to the nearest tenth of a day.