second dilution question - urgent (Dec/07/2010 )

Can someone help me with this?

I have stock DNA at different concentrations, but I can bring them all down to a specific concentration. I am having trouble figuring out what this concentration should be.

I will be making a reaction where 1ul of the DNA at that specific concentration is added into the reaction. The volume of DNA added has to be 1ul, and the final concentration of DNA in reaction has to be 500ng/50ul (or 10ng/ul). What concentration do I bring the stock DNA down to in order to do all of this?

Even the formula will be fine.

What is the total amount of DNA needed in your reaction?
Answer: 500 ng (the volume, 50 ul is irrelevant)

What is the total volume being added that must contain that DNA?
Answer: 1 ul

I need 500 ng in 1 ul, so 500 ng/ul

Arithmetic.