-- Take a sample of the first fluid. -- Measure its mass. -- Measure its volume. -- Divide its mass by its volume. This gives you the density of the first fluid.
-- Take a sample of the second fluid. -- Measure its mass. -- Measure its volume. -- Divide its mass by its volume. This gives you the density of the second fluid.
You want their average ? OK
-- Add (Density of the first fluid) + (Density of the second fluid). -- Divide the sum by 2 .
Now you have the average of the two densities.
Note: That's NOT necessarily the density of a mixture when you pour some of fluid-1 and fluid-2 into a jar. The density of the fluid in the jar is going to depend on how much of each fluid is in there. I started to calculate how much of each one has to be there in order for the density of the mixture to be equal to the average of their two densities. But then I sat up straight, asked myself "Why ? !" . Then I stopped, and went into the kitchen and ate some meatloaf.
