That's not how it works. Each core runs at 1.3Ghz, but you don't add those numbers together to get a total. It helps to understand how a multi-core processor works. Each core runs independently of the other. If you send a single instruction to the processor, it will get processed by only one of the cores, but not both. In other words, this single instruction would not run twice as fast on a 2 core processor versus a single core processor.
This doesn't mean having 2 cores is pointless though. When you are browsing the web and working on a Word document, one core can be handling instructions from the web browser, while the other handles instructions from Word. Also, some applications are programmed such that they can make good use of multiple cores. Typically applications that do a lot of intensive data crunching will fall under this scenario, such as audio/video editing applications.