If two miscible liquids of same volume but different densities Px and P2 are mixed, then the density of the mixture is given by

Density is defined as the ratio of mass to volume. When two miscible liquids of the same volume (V) but different densities (Px and P2) are mixed, the total mass of the mixture is the sum of the individual masses. The mass of the first liquid is PxV and the mass of the second liquid is P2V. Therefore, the total mass of the mixture is (Px + P2)V. Assuming the liquids are miscible and the total volume is the sum of individual volumes, the total volume of the mixture is 2V. The density of the mixture is calculated by dividing the total mass by the total volume: (PxV + P2V) / 2V. This simplifies to (Px + P2) / 2, which is the arithmetic mean of the two densities.

Sources

1. [1] Science ,Class VIII . NCERT(Revised ed 2025) > Chapter 9: The Amazing World of Solutes, Solvents, and Solutions > How do scientists define density? > p. 140