Lessons · Pharmacy · millilitres an hour
Millilitres an hour
The rate on the pump is the volume divided by the time in hours.
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
The bag arrives with a volume on it and an order that says how long it should run. The pump wants one number, in millilitres an hour, and it is the only number that has to be typed in correctly for the bag to finish when it is supposed to.
How to think about it
Put the time in hours before dividing. Minutes become hours by dividing by 60, so 30 minutes is 0.5 h and 45 minutes is 0.75 h. Then volume over hours, and the unit that comes out is mL/h.
Worked example
Rate = volume / time in hoursThe whole formula.
1,000 mL over 10 h = 100 mL/hA litre over ten hours.
500 mL over 5 h = 100 mL/hHalf the bag over half the time is the same rate.
250 mL over 30 min = 250 / 0.5 = 500 mL/hMinutes into hours first: half an hour, not thirty.
Your turn
A 600 mL bag is to run over 5 hours. Write the rate.
600 / 5 = mL/h
Solve one, graded on the server
The trap
Dividing by the minutes. 250 mL over 30 minutes is not 8.3 mL/h; the formula wants hours, and leaving minutes in makes the rate sixty times too small.