What do you need to dilute to make a 1:5 dilution of serum sample?

The great thing about ratio is that it is easy to understand. Since it says that you need 1:5, you just need to immediately look at the numbers of the choices. A says 1.0 ml of serum with 5.0 ml of diluent. When transformed to ratio, this signifies 1:5.

The other choices obviously do not have the same numbers which mean that they are not the answers that you are searching for. The ratio can be as simple as possible and you will get the answer that you are searching for.