For the first-order reaction ${\mathrm{T}}_{av}$ (average life), ${\mathrm{T}}_{50}$ and ${\mathrm{T}}_{75}$ in the increasing order are :

The average temperature with respect to rate constant,

$T_{\text{avg }}=\frac{1}{K}=1.44T_{1/2}$

The time taken ${\mathrm{T}}_{50}$ is half then time taken for ${\mathrm{T}}_{75}$.

$T_{3/4}=2\times T_{1/2}$