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:

1. 15

2. 05

3. zero

4. 10

A country with a high rate of population growth took measures to reduce it. The figure below shows age-sex pyramids of populations. A and B are twenty years apart. Select the correct interpretation about them: 
 
Interpretations