Lessons · Pharmacy · eye drops, at 20 drops to the millilitre
Eye drops, at 20 drops to the millilitre
Using 20 drops per mL as the problem gives it, a bottle holds its millilitres times 20 drops, and the days' supply is those drops divided by the drops used in a day.
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.
In beta. This lesson was written for Hone and has not yet been checked by a licensed pharmacist. Practice material, not professional advice. What that means.
What it is for
A drop bottle is the one container nobody can count by eye, and the plan still wants a days' supply. The other half of it is the second eye: a sig that says each eye uses twice as many drops as a reading that forgets.
How to think about it
Drops in the bottle: millilitres times drops per millilitre. Drops in a day: drops per eye, times the number of eyes, times how many times a day. Divide, and round DOWN.
Worked example
1 mL = 20 dropsThe figure the problem gives you. Never assume one.
A 10 mL bottle x 20 drops/mL = 200 dropsVolume times drops per millilitre.
1 drop in each eye twice a day = 1 x 2 x 2 = 4 drops a dayThe second eye doubles the count.
200 / 4 = 50 daysBottle divided by a day's worth, rounded DOWN to whole days.
Your turn
A 15 mL bottle at 20 drops per mL. Write the number of drops it holds.
15 x 20 = drops
Solve one, graded on the server
The trap
Forgetting the second eye. A sig that says each eye uses exactly twice what a one-eye reading gives, and the days' supply comes out twice as long as it really is.