The doubling time

A population grows by the same share every year. You will write the growth, count the years to doubling in a loop, and compare the answer with the rule of 70.

The idea. Each year the population is multiplied by $1 + \dfrac{r}{100}$. The doubling time is the number of years until the population is at least twice the start.

Your tasks.

1. Finish population. It gives the population after years.
2. Finish years_to_double. It counts the years in a loop until the population is at least twice the start.
3. Finish rule_of_70. It gives $70$ divided by the rate.