Why do you think people who live at high altitudes are advised to add salt to water when boiling...

Why do you think people who live at high altitudes are advised to add salt to water when boiling food like pasta? What mole fraction of NaCl is needed to raise the boiling point of H₂O by 3째C? Does the amount of salt added to water (typically about one teaspoon to four quarts of water) substantially change the boiling point? K_b (H₂O) = 0.51째C/molal.