Two liquids of densities 1.2gm/cc and 1.4gm/cc are mixed with a proportion of their volumes equal to 1: 2. What is the density of the resulting liquid?

Given, ρ₁ = 1.2 gm/cc and ρ₂ = 1.4 gm/cc 

Let the volume of the first liquid be V₁ = 1x

Let the volume of the second liquid be V₂ = 2x

Mass of the first liquid, m₁ = ρ₁ V₁ = 1.2 x

Mass of the first liquid, m₂ = ρ₂ V₂ = 2.8 x

We know, 

$\begin{array}{rcl}\mathrm{Density}, \mathrm{\rho } & =& \frac{\mathbf{Total}\mathbf{ }\mathbf{mass}}{\mathbf{Toal}\mathbf{ }\mathbf{volume}}\\ & =& \frac{{\mathrm{m}}_1+{\mathrm{m}}_2}{{\mathrm{V}}_1+{\mathrm{V}}_2}\\ & =& \frac{1.2\mathrm{x}+2.8\mathrm{x}}{1\mathrm{x}+2\mathrm{x}}\\ & =& \frac{4}{3}\\ & =& \mathbf{1}\mathbf{.}\mathbf{33}\mathbf{ }\mathbf{gm}\mathbf{/}\mathbf{cc}\end{array}$