$(1)$ A typical mud is $70wt\%$ sand, balance water. What is its density near RT if ${}_{\text{s}\text{a}\text{n}\text{d}}=2300k\frac{g}{m^3}?$ Why is the first equation correct over the second one? My professor states to check the units, but all I see is two ratios, which are dimensionless. I don't understand his use of the first equation.