Im really bad and math would like some clarification, on addgene it states "to dilute your antibiotic into your LB medium at 1:1,000. For example, to make 100 mL of LB/ampicillin growth media, add 100 μL of a 100 mg/mL ampicillin stock (1000X stock) to 100 mL of LB".

But shouldn't it be into 99.9 ml to be a 1:1000. Im confused as shouldn't we minus the stock from the total to add the dilutent reagent? When we use C1V1=C2V2 we minus so why not here?

Thank you so much!