# Math Help - Half-life

1. ## Half-life

An isotope has a half-life of 65 min. If the decay is modeled by the differential equation dy/dt = -ky, where t is measured in minutes, what is the decay constant k?

Can someone explain this to me? What I have to do, and why?
Greatly appreciated!

2. $\frac{dy}{dt}=y'=-ky \Rightarrow \frac{y'}{y}=-k$

Then, you can integrate both sides respect to time, and use the given condition to determinate the constants.