Why is a dualcore 2.8GHz slower than an LGA 3.00GHz?

i have both types of processors in my university, and i found that the normal 3.00 ghz one is faster than the 2.8 dualcore? (note that they both have 2 gb ram with same disk space and everything the same even the mother board.)
i am going to buy a new processor and of course the 3 ghz one is much cheaper,
so is it really true that a 3ghz is faster than the dualcore one?
thanks
Answer #1
If the 3ghz is a normal single core pentium cpu it will be slower then the core 2 duo
Answer #2
No, the dual core will be faster when running at 100% efficiency
Answer #3
ok, thanks