Estimate the average annual growth rate of the world population for 1950, 1988, and 2010 using model 17 from the previous page.

model 17. year population growth rate (%)
1972 1.96
1982 1.73
1992 1.5
2002 1.22

Although I don't see 1950, 1988, or 2010 on your model, I did calculate the average for 1972, 1982, 1992, and 2002: the average that I got was 1.6025 (this answer has not been rounded due to the fact that I don't know if you need to round it)
hope this helps

1/2 or .5

Divide 3 on both sides