Name: Sandy

Who is asking: Teacher
Level: All

Question:
A colleague and I have a disagreement about dilutions. I seem to remember that I was taught (although it was a long time ago) that a RATIO was written thusly: 1:5 , and read " one part to five parts", for a total of 6 parts. On the other hand, a fraction is written: 1/5 and is read" one part in five" for a total of 5 parts. My colleague says that the ratio reads "one part in five" and is essentially the same as a fraction. Which is right? Have I been doing dilutions wrong all this time? I teach Animal Nursing and need to know where I can find a consise answer to such questions for making up medicated fluids, etc. Thank you.

You are correct. If you make salad dressing with vinegar and oil in the ratio of 1:5, then you put in 1 ml of vinegar and 5 ml of oil to get 6 ml of salad dressing. The resulting dressing is composed of one-sixth vinegar and five-sixths oil. I would read the "1:5" notation by saying that the dressing has vinegar and oil in the ratio of one to five.