\[\text {Total Hardness }= \left[\left\{\frac{\left[\text{Ca}^{2+}\right]}{\text { Equivalent weight of } \text{Ca}^{2+}}\right\} \times \text { Equivalent weight of } \text{CaCO}_{3}\right]+ \left[\left\{\frac{\left[M g^{2+}\right]}{\text { Equivalent weight of } M g^{2+}}\right\} \times \text { Equivalent weight of } \text{CaCO}_{3}\right]\]
\[\text { Total hardness }=\left[\frac{\left[\text{Ca}^{2-}\right]}{20} \times 50+\frac{\left[\text{Mg}^{2+}\right]}{12} \times 50\right]\]