Lessons · Pharmacy · how long the bag will run
How long the bag will run
The time is the volume divided by the rate, which is the millilitres-an-hour relationship turned around.
Hone is a place to practise a career, one idea a day. This is one of its lessons, written out in full and free to read without an account.
What it is for
Somebody hangs a bag and somebody else has to know when it needs changing. A time that is half an hour out is a pump alarming in the middle of the night, and the arithmetic that prevents it is one division.
How to think about it
Volume over rate gives hours. If it comes out with a fraction, multiply the fraction by 60 to say it in minutes. To get the finish time, add the hours to the clock time it was hung.
Worked example
Time = volume / rateThe same relationship, turned around.
1,000 mL at 125 mL/h = 8 hThe bag hung at breakfast is done in the afternoon.
50 mL at 100 mL/h = 0.5 h = 30 minA small bag. Turn the fraction of an hour into minutes.
Hung at 09:00 and running 8 h: done at 17:00Add the hours to the clock.
Your turn
A 750 mL bag is running at 250 mL/h. Write the time it will take, in hours.
750 / 250 = h
Solve one, graded on the server
The trap
Dividing the rate by the volume. The answer comes out as a fraction of an hour on a bag that is going to run all day, and it looks like a small tidy number.