Two radioactive substances X and Y originally have N1 and N2 nuclei respectively. Half life of X is half of the half life of Y. After three half lives of Y, number of nuclei of both are equal. The ratio N1N2 will be equal to:

Given : Tx=Ty2   ⇒1λx=12λy  ⇒λx=2λy  At, t=3Ty  Nx=N1e-λx3Ty       and Ny=N2e-λy3Ty        Given :   Nx=Ny                                          ⇒N1e-λx3Ty=N2e-λy3Ty  ⇒N1e-λx×3ln2λy=N2e-λy×3ln2λy  ⇒N1e-6ln(2)=N2e-3ln(2) ⇒N1N2=e3ln(2)=8