Suppose the decay for a radioactive element is known to be y=y e^-0.24t, with t in years. About how long will it take for a sample of this element to decay to 70% of its original amount?
Suppose the decay for a radioactive element is known to be y=y e^-0.24t, with t in years. About how long will it take for a sample of this element to decay to 70% of its original amount?
I assume you mean $\displaystyle y = {\color{red}y_0} e^{-0.24t}$.
The initial amount is $\displaystyle y_0$. So substitute $\displaystyle y = 0.7 y_0$ and solve for $\displaystyle t$: