Scary Real Life Math Stories


Or, Why Rates And Proportions Are Important.

It’s Monday morning.  I am having a medical procedure done in which medicine is pumped into my arm through an IV.  My nurse is calm, efficient, and experienced.  She is also training someone new.  No problem: Everyone is new at one time or another.

After the experienced nurse inserts the IV, the two nurses leave me to retrieve the medicine.  This is the gist of the the conversation I hear through the curtain:

The amount of medicine is 100 ml and it needs to be infused over half an hour.  The machine needs the infusion rate to be entered in ml per hour.  What rate should you enter on the machine?


The medicine is 100 ml and it needs to be delivered in half an hour.  What do you enter on the machine?


Think.  We have to infuse the entire 100 ml in only half an hour.  How many ml/hr do we need to enter on the machine?

Oh, 200!



You can be sure I was paying close attention to this conversation.  And even though the trainee eventually got to the right answer, I was still relieved to see the experienced nurse check the machine.

One thing I noticed:  The strategy employed by the experienced nurse was essentially to repeat the question, with very little modification, and to calmly ask the trainee to “think.”

My approach would have been different.  When the trainee first answered “100,” I would have said something like, let’s think about that.  If we enter 100 ml/hr into the machine, and we have 100 ml of medicine, how long will it take the medicine to be completely infused?  I presume the trainee would have said it would take an hour.  (At least I hope so.)  At that point, I would have said, now if we want to infuse the medicine in half that time, do we need a faster rate or a slower rate?  What rate do we need to enter?  

I think this approach would have made a better connection for the trainee and allow her to see how her answer needed to change.  It would also better model the thinking needed to solve the problem.

What would be an even better way to have handled this situation?


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