Finding the percentage of pure CaCO3
The question is a bit poorly written. But it also gives a sense to the procedure of dissolution of chalk upon treatment with $\ce{HCl}$ and dilution of the solution.

The reaction that takes place after the treatment with $\ce{HCl}$ is;

$\ce{CaCO3}$+ 2$\ce{HCl}$ → $\ce{CaCl2}$ + $\ce{H2CO3}$

$\ce{H2CO3}$ decomposes into $\ce{H2O}$ and $\ce{CO2}$.
$\ce{CO2}$  is a gas. It bubbles up out of the solution. 

$\ce{CaCl2}$ is soluble in water. So it should be dissolved by adding water.Further, it should then be diluted to the required volume.

"The chalk was dissolved" might signify the addition of water to dissolve the water soluble $\ce{CaCl2}$ produced during chemical reation with $\ce{HCl}$.