You have a 100 ml stock solution of 100 mg/ml ampicillin in deionized water. You want to make 30 ml of 25 mg/ml ampicillin in deionized water. How much ampicillin stock and how much deionized water are needed to make this

The amount of  ampicillin stock is  

The amount of deionized  is 22.5 \ mL

Explanation:

From the question we are told that

   The volume of stock solution of ampicillin in de-ionized water is

   The concentration (in mg ) of ampicillin in de-ionized is

    The volume of ampicillin in deionized water to produce is

The concentration (in mg )  of ampicillin in de-ionized water to produce is

The chemical process can be mathematically represented as

=>          

The amount of  ampicillin stock is   and amount of 25 mL  (30 - 7.5 = 22.5 mL ) of deionized water

what is the question here. i think you messed up.