Problem

Two radioactive materials

X_1

and

X_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

X_1

to that of

X_2

will be

1/e

after a time (JEE 2000) a.

1/10\lambda

1/11\lambda

11/10\lambda

1/9\lambda