The average person in the US reads at below a high school level. How do you explain to someone who doesn't understand high school level writing, let alone math

The average person in the US reads at below a high school level. How do you explain to someone who doesn't understand high school level writing, let alone math, that "No, you can't just say Pi is 4, it doesn't work like that" in a way that they will agree in the end, rather than just calling you an elitist shithead who is patronizing them?