I am currently working on a project, a sample start-up. Suppose I have these data:
$N$ = total population.
$n_1$ = number of mall shoppers.
$n_2$ = number of people aged from 18-65.
$n_3$ = number of people with smartphones.
The question is how do I get the number of mall shoppers who are aged 18-65 and also have smartphones from the total population of the country? This number would then result to the approximate target audience for my start-up project but I don't know how to get it.