These are college graduates.
> Does a solid knowledge of, e,g, Set Theory, give any benefit later in life?
Knowledge of statistics will help a person a lot.
Another example. I wanted to put an elliptical brick patio in my yard. The contractor gave a square footage and I signed a deal with the charge per square foot. He staked it out.
It looked a bit peculiar to me. So I measured the major and minor axes and computed the area of the ellipse. It was 1/3 smaller than the contracted amount. The pallet of bricks was sitting in the driveway. I multiplied xyz to get the square footage of the bricks, and walla, it matched the area staked out.
I.e. I was being cheated. The contractor evidently was used to math challenged customers, and discovered how much he could cheat before being noticed. I pointed out the "error" (hahahaha) and the contractor reduced the bill by a third.
> why don't we teach that?
Exactly!
I'll add that math isn't really just about that sort of practicality though. It's also about a fundamental understanding of numbers and what they mean.
For example, inflation is in the news a lot. It's high, or low. Most people (the US president included) think that if inflation was 0% prices would come down. But that'd be a profound misunderstanding of the topic.
A grounding in numbers, in this case percentages, makes for a better understanding.
Any business owner needs to know fundamental truths to survive. Cost price, markup, margin, selling price, fixed expenses versus variable expenses and so on. All are grounded in basic math. Without that you can't do basic accounting. Without that you can't effectively run a business.
Anti-vax arguments are built on very bad math, and people bad at math fall for it.
We all use math all the time. People bad at math are at a major disadvantage. Populations bad at math are easily manipulated.