How do I explain to my dad that a 1.5 ghz dual core is not a 3.0 ghz single core?

To him, he thinks that (clock speed) * (# of cores) = "total" clock speed.

So a 2.2 ghz dual core is not a machine that clocks at 4.4 ghz and a 1.8 ghz quad core is not a 7.2 ghz beast.