Calculating Molar Concentration

Molar concentration is the number of moles contained in one litre of a substance. The concentration of a solution is expressed in |\text {mol/L}.|

|C=\dfrac{n}{V}| 
where
|C| stands for molar concentration |\text {(mol/L or M)}|
|n| stands for the number of moles |\text {(mol)}|
|V| stands for the volume of the solution |\text {(L)}|

What is the molar concentration of a solution if |20\ \text {g}| of |CaCO_{3}| were dissolved in |500\ \text {mL}| of solution?

Here are the given values of the problem.
||\begin{align} m &= \text {20 g} &V &= \text {500 mL = 0.500 L} \\ M &= \text {100.09 g/mol} &C&= \text {?} \end{align}||
First the mass must be converted into moles.
||\begin{align} n= \dfrac{m}{M} \quad \Rightarrow \quad n &= \dfrac{\text {20 g}}{\text {100.09 g/mol}} \\ &= \text {0.2 mol} \end{align}||
It is then possible to determine the concentration of  |\text {mol/L}| using the formula.
||\begin{align} C =\dfrac{n}{V} \quad \Rightarrow \quad
C&=\dfrac {\text {0.2 mol}}{\text{0.5 L}} \\ &= \text {0.4 mol/L = 0.4 M} \end{align}||