Maybe stupid question..(primers)

[ineska]

hi there..
it's a little bit stupid question but I have to make sure..
about primer concentration:
I have 30nM of lyophilized primer, I add 300 ul water or TE buffer and get 100uM/L stock solution. If I add 600 ul water I get 200uM/L stock solution???
So to prepare 10uM/L work solution I have to take 20ul primer stock solution and add 80 ul water?? Am I right? Question is cause I did the dilution one more time after did it the first one...
thank You in advance!!!

[butters]

30nM + 300ul water = 300ul of 100uM stock solution.

*if 30nM + 600ul water = 600ul of 50uM stock solution
**remember what ever amount of water you added you only have 30nM of primer

To prepare 10uM of primer you need
1 in 10 dilution for 100uM (10ul + 90ul of water)
or
1 in 5 dilution for 50uM (20ul + 80ul of water)

if you add 600ul then u would need from stock 20ul + 80ul of water.