Question 107368
You can use a compound interest formula for this problem even though its not money but people>......

{{{A=P(1+r/100)^n}}}

where p is the initial population, r is the rate of increase and A is the final population. We want the time in years, n.

So we know that
{{{64000=32000(1+3.2/100)^n}}}

dividing through by 32000

{{{2=(1.032)^n}}}

take log of both sides

{{{log2=nlog1.032}}}
{{{n=log2/log1.032}}}

n=22years