Yep, what does your mechanic know about geometry today? If he can't explain the fundamentals of the Pythagorean theorem then he doesn't know squat about that math and you taught him nothing........Nice try.
I didn't claim to have taught him geometry. The lesson I wanted to teach him was the value of education. He was very explicitly appreciative of not having to go through exactly the same exercise five times and he realized that understanding the geometry of the situation would have allowed him to do the job ONCE.
He realized that he didn't have to simply guess the answer. There was a high-school-level solution that he could have used.