Given that the initial population, $N_0$ of bacteria is $12$ and the population doubles every $20$ minutes. I wish to find a general formula for the population if one unit of time is $50$ minutes for $t=0,1,2,3,\ldots$.
If one unit of time is $20$ minutes, then I can 'easily' find $N(t)=12\cdot 2^t,~t=0,1,2,\ldots$.
How do I solve the original problem? Is there a general method for approaching these types of questions?