The standard formula for radioactive decay, as you know, is $N(t)=N_02^{-t/h}$, where $N_0$ is the initial amount, $t$ is the time elapsed, and $h$ is the half-life (with $h$ and $t$ being measured in consistent units). So for the material to reach 1% of its initial value, $\frac{N}{N_0}=.01$. Therefore, simply isolate t in the following equation: $.01=2^{-t/30}$