chemistry dilution
posted by Reese .
Given VLP with concentration 200ug/mL, dilute to 3ug/100ul.
Please help me with this; many thanks

Add 6.67 x 10^1 mL of solvent to 1mL of stock.
Converting everything to ug/mL, 200/3 =6.67 x 10^5 uL or 6.67 x 10^1 mL
200ug/(6.67 x 10^5 mL +1 mL)= 2.96ug/mL 
Typos
Add 6.67 x 10^1 mL of solvent to 1mL of stock.
Converting everything to ug/mL, 200/3 =6.67 x 10^1 mL
200ug/(6.67 x 10^1 mL +1 mL)= 2.96ug/mL 
Did it again,
Add 5.67mL of solvent to 1mL of stock to get a total volume of 6.67mL.
Converting everything to ug/mL, 200/30 =6.67mL
200ug/(5.67mL +1 mL)= 29.9ug/mL 
This is a confusing problem.
Here is another approach.
We have a soln that is 200 ug/mL.
We want 3 ug/100 uL. That is
0.003 ug/uL = 3 ug/mL
Say we want to make 100 mL of this solution, then 3 ug/mL x 100 mL = 300 ug we need.
200 ug/mL x ?mL =300 ug
?mL = 300/200 = 1.5 mL;
Therefore 1.5 mL of the 200 ug/mL solution and dilute that to 100 mL to make 300 ug/100 mL (which is 3 ug/mL). I think this is easier than measuring 5.67 mL of anything, expecially since we could use a 100 mL volumetric flask. 
That is way easier, but I thought this may just be a homework problem and not a lab/research problem. So, I thought this would suffice. But, if you have to keep doing this dilution using 1.5mL compared to 1 mL of solution can get expensive, especially when research funds get tight or your PI has a bird mentality like mines did; cheap, cheap, cheap.

And I think one of us messed up. Either it should be 3ug/mL or 30ug/mL. When I punch in your numbers I get 15mL not 1.5mL.
My work:
3ug/100uL=3 x 10^2 ug/uL
3 x 10^2 ug/uL*(1uL/10^3mL)= 3 x10^1 ug/mL=30ug/mL.
I could be wrong though. 
thanks Devron and DrBo222