During the titration of a mixture of ${\text{Na}}_{\text{2}}{\text{CO}}_{\text{3}}{\text{\hspace{0.17em}and\hspace{0.17em}NaHCO}}_{\text{3}}$ with HCl using phenolphthalein and methyl orange indicators simultaneously 

Disappearance of pink – violet colour corresponds to the conversion of ${\text{Na}}_{\text{2}}{\text{CO}}_{\text{3}}{\text{\hspace{0.17em}to\hspace{0.17em}NaHCO}}_{\text{3}}$

Appearance of red colour corresponds to the complete decomposition of ${\text{NaHCO}}_3$ previously

Disappearance of pink – violet colour corresponds to the neutralization of ${\text{NaHCO}}_3$

Appearance of red colour corresponds to the decomposition of ${\text{NaHCO}}_{\text{3}}$ formed and that previously present