The potato core will gain mass in a sugar-water solution that has a lower concentration of sugar than its own internal concentration (10%).
The Concentration Gradient: for this case, the potato core (10% sugar) has a higher concentration of sugar than the surrounding solution. This creates a concentration gradient for water. Water molecules will naturally move across the potato cell membrane, from the solution (low sugar concentration) into the potato core (high sugar concentration), trying to even out the concentration difference.