The accepted formula for figuring drops per minute is: amount to be infused in one hour × drop factor/time for infusion (min)= drops per minute. Using this formula: 1,000/8 hours = 125 ml/ hour 125 × 10 (drip factor) = 1,250 drops in one hour. 1,250/ 60 (number of minutes in one hour) = 20.8 or 21 gtt/min (C).Correct Answer: C