In a radioactive decay sequence
$\mathrm{A}\stackrel{{\mathrm{\lambda }}_1}{\to }\mathrm{B}\stackrel{{\mathrm{\lambda }}_2}{\to }\mathrm{C}\stackrel{{\mathrm{\lambda }}_3}{\to }\mathrm{D}$
What is the ratio of numbers of atoms of A to the number of atoms of B after long time interval starting with pure A. The mean lives of A and B are 20 hours and 30 minutes respectively.