Two radioactive materials $ X_1\: and\: X_2$ have decay constants $ 5\lambda\: and\: \lambda$ respectively. If initially they have the same number of nuclei, then the ratio of the number of nuclei of $ X_1$ to that of $ X_2$ will be $ \large\frac{1}{e}$ after a time : - Clay6.com, a Free resource for your JEE, AIPMT and Board Exam preparation

Two radioactive materials $ X_1\: and\: X_2$ have decay constants $ 5\lambda\: and\: \lambda$ respectively. If initially they have the same number of nuclei, then the ratio of the number of nuclei of $ X_1$ to that of $ X_2$ will be $ \large\frac{1}{e}$ after a time :