\(\displaystyle{y}={a}{\left(\frac{{1}}{{2}}\right)}^{{t}}\)

This is a decay function

Rate of decay is \(1-0.5=0.5\)

That is 50%

Consider an exponential function of the form: \(\displaystyle{y}={b}\cdot{a}^{{x}}\)

If a>1, then it is exponential growth function with growth rate \(a-1\)

If a<1, then it is exponential decay function with decay rate \(1-a\)