Acell is in a soulution with the simple sugar glucose. the concentration of glucose outside the cell is 30% and the concentration of glucose inside the cell is 20%

In this situation, water molecules will flow from the cell inside into the solution outside, due to osmosis.
Osmosis is always the water molecules flowing from a region of higher water potential to a region of lower water potential, across a semi permeable membrane, which is the cell membrane here.
As the glucose concentration is higher, this also means that the water potential of it is lower.
Water will keep flowing out until equilibrium is reached, ie. The water potential is same for both sides.
When water flows out from the cells, the cell will shrink because it lose so much water.
In addition, if the cell is plant cell, the cell membrane may detach from the cell wall, and plasmolysis occurs.