Does A Dual Core Processor Rated At 2.4 G.H. Mean Both Processors Work At 2.4 G.H. Or Combine To Work At That Speed?

Combine to work at 2.4GHz who evr tells you its double do not  belive  the intel pentium Ds combine to that speed and the core 2 duos and quads  have 2 or 4 runing at 2.4ghz but they do not all add up