There are many ways to think about this question, but the technique I want to focus on is something called Fermi estimates, which were highlighted in one of my recent textbook readings. If you have ever heard the phrase "back-of-the-envelope" calculation, then you have inadvertently heard of Fermi estimates. They are championed as a great way to get students to learn math because they have to go beyond regurgitating formulas and actually think deeply to approach a problem.
Whilst the label "Fermi estimate" is new to me, I've actually been exposed to these kinds of ideas for a long time. They are an old-time favourite for interviews at consulting firms, and I would often pose Fermi problems when interviewing financial modelling candidates (my go-to options being how many gravediggers in Australia, and how many planes in the sky).
Almost by coincidence, right after doing my reading on Fermi estimates I encountered Numberphile's recent video on calculating how much coronavirus there is in the world, where they use the technique to argue that all of the world's SARS-CoV-2 particles would fit into a single can of Coke. Tick, boom! You can check it out here: