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# Which of the following is correct:-($N_t$=Population at time t,$N_{t+1}$=Population after a unit,$B$=Natality,D=Mortality,I=Immigration time,E=Emigration)

$\begin{array}{1 1}(a)\;N_{t+1}=N_t+[(B+I)-D+E)]\\(b)\;N_t=N_{t+1}+[(B+I)-(D+E)]\\(c)\;N_{t+1}=N_t+[(D+E)-(B+I)]\\(d)\;N_t=N_{t+1}+[(B+D)-(E+I)]\end{array}$

$N_{t+1}=N_t+[(B+I)-D+E)]$ is correct.
Hence (a) is the correct answer.