a) The population size of a country is increasing at a rate

of 4% per year. How long does it take until the country has doubled
its population size?
b) The number of new flu cases is decreasing at a rate of 5% per week.
After how much time will the number of new flu cases reach a quarter
of its current level?

1 answer

1.04^n =2
n log 1.04 = log 2
n = log 2 / log 1.04

second one same way
0.95^n = 0.25