Question

If the world’s population is increasing at an annual rate of 1.3%, and there were 5 billion people in the year 1986, then in what year will the world’s population be 10 billion?

Answer 1

5 billion * ( 1 + 0.013 ) ^x = 10 billion
1.013 ^x = 10 : 5 = 2
$x = log_{1.013}2$
x = 54
1986 + 54 = 2040
In the year 2040 the world`s population will be 10 billion.