Interview Question for Business Analyst at Acquity Group:

There is no "right" answer. Just trying to figure out how to sort through large amounts of data and if you know how to think logically and critically.

Cross reference paint store transactions with commercial business licenses?

This is just a way of determining your thought process in solving problems. It's the procedure - the answer doesn't really mean anything

It's all process and reasoning. Something like:

There are 300 million people in the US, and let's say 50% of them live in a house, at 3 people per house on average. So there are 50 million houses in the US. Each house gets repainted every 10 years on average, so 5 million houses get painted each year.

Each house takes 5 days so each house painter can paint say 20 houses per year (since you can't paint during the winter, and also many painters do it just as a summer job).

5 million houses get painted each year and each painter does 20, so there are about 250,000 house painters .

Just check the latest census data... and extrapolate from there.

Cecil has the correct approach, this type of problem is known as a "Fermi" problem - you can look it up.
My numbers were 120 million houses, they get painted every 10 years, 1 guy paints 40 houses per year (remember interiors take less time) so 12M/40=300,000 house painters in the US, 20% more than Cecil's estimate