A biologist studied the population of rats in a barn. He found that the average natality was 250, average mortality 240, immigration 20 and emigration 30. The net increase in populations is :

A biologist studies the population of rats in a barn. He found that the average natality was 250, average mortality 240, immigration 20 and emigration 30. The net increase in population is :

A biologist studied the population of rats in a barn. He found that the average natalty was 250, average mortality 240, immigration 20 and emigration 30. The net increase in populations is:

A biologist studied the population of rats in a barn . He found that the average natality was 250 , average mortality 240 , immigration 20 and emigration 30. The net increase in population is :