Two radioactive materials ${\text{X}}_{\text{1}}$ and ${\text{X}}_{\text{2}}$ have decay constants $10\lambda$ and $\lambda$ respectively. If initially they have the same number of nuclei, then the ratio of the number of nuclei of ${\text{X}}_{\text{1}}$ to that of ${\text{X}}_{\text{2}}$ will be $1/\text{e}$ after time