Med Math: Drop Factors Question #7


The same IV orders above (500 mL NS over 5 hours) will have how many mL left in the IV bag in 3 hours?


  1. 200 mL
    • Rationale:
  2. 300 mL
    • Rationale:
  3. 150 mL
    • Rationale:
  4. 55 mL/hr
    • Rationale:



Normal Saline is to be infused. You would need to know how much volume in ml you need per hour in order to solve. The total volume is set at 500 ml to be infused for required time. The hour is not converted to minutes to solve the problem. The 500 ml to be infused is divided by 5 hours. There is a simple formula below for calculating the flow rate. Then the volume left needs to be calculated. If 500 ml is the total and 300 ml was infused you would have 200 left. The final answer should have ml within.


—– x 1 (understood to be 1 as in 1 hour) = Total volume per hour_100__ml/hr


Total volume per hour x total hours already infused= Total Volume infused for required time

Total Ml/hr_100___x Total infused hours allready_3___= Total volume infused so far_300____ML

Total Volume is set for required time subtracted by infused volume= Volume left to be infused

Total volume_500 ml_ – infused volume__300 ml = _200___ ML left to infuse

100 ml/hr x 3 hrs = 300 ml infused in 3 hours so 200 mL is left

Learning Outcomes

Test Taking Tip

Video Rationale