Question

What volume of alcohol with the density of 8.4×10²kg/m³ will have the same mass as 4.2m³ of petrol whose density is 7.2×10²kg/m³

Answer 1

The mass of substance is related with density and volume as follows

$$m=\rho V$$

So

$$\rho_1V_1=\rho_2V_2$$

$$V_2=V_1\frac{\rho_1}{\rho_2}$$

$$=4.2\:\rm{m^3}\times\frac{7.2\times 10^2\:\rm{kg/m^3}}{8.4\times 10^2\:\rm{kg/m^3}}$$

$$=3.6\:\rm{m^3}$$