Two radioactive elements X and Y have decay constantsλ and 10λ respectively. If decay begins with the same number of atoms of them, the ratio of atoms of X to those of Y after time 19λ will be
e
Nx=N0e−λt=N0e−λ9λ=N0e−19Ny=N0e−10λt=N0e−10λ9λ=N0e−109Hence,NxNy=e−19−109=e