The half life period of a radioactive element X is same as the mean life time of another radioactive element Y. Initially both of them have the same number of atoms. Then

T1/2x=tmeany ⇒0.693λx=1λy⇒λx=0.693λy or λx < λyAlso rate of decay = λNInitially number of atoms (N) of both are equal but since λy>λx, therefore, y will decay at a faster rate than x.