Yes: V+V 1 = 1L (total volume in the bottle).

Let the inner radius of the bottle body part be r and the inner bottom radius of the cylindrical cup be r.

Then it is: V/Pi*R*R = 2 (when the bottle is placed upright, the height of water is less than 2 decimeters).

V 1/Pi*R*R = 0.5 (when inverted, the height of spare parts is less than 0.5 decimeter).

The volume v of water can be solved by the above three equations:

V = 0.8L L.

Then look inside the cylindrical glass:

V/Pi*r*r = 1 (water level in cylindrical cup 1 decimeter high).

According to this equation, the inner bottom area r of cylindrical water cup can be obtained:

R = 5.05 cm