Hurst Review 5th Day CD-ROM Math question

Could anyone please tell me how the hurst review came up with 125mg/125ml for the final concentration in this problem. I understand the entire equation except for that part. I don't know how they get 125ml when adding to a 100ml bag.

Please help, thanks.

To calculate does with infusion already in progress:
________mg/ml X _________ml/h = ______ mg/h
Concentration pump setting dosage
Example: Calculate the IV infusion rate in ml/h for a 70 kg patient requiring dilitiazem, 5 mg/h. Dilitiazem is in a single use vial with a concentration of 125mg/5 ml. It should be added to 100 ml D5W to make the final infusion solution.

Calculation: Dilitiazem 125 mg = 5mg + 100 ml D5W = 100 ml
Final concentration: 125 mg/125ml = 1 mg/ml
Answer: setting the infusion pump at 5 ml/h will result in a final infusion rate of 5 mg/h