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.
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.