When a glass rod is rubbed with silk, it becomes positive and the silk becomes negative—yet both attract dust. Does the dust have a third type of charge that is attracted to both positive and negative? Explain. g

The dust does have any third charge.

Explanation:

                In the context, the glass rod gets positively charged and so it induces a negative charge on the dust particles which are neutral. Thus the face of the dust particle which is near to the rod becomes negative charge and the opposite face of the dust gets equal positive charge and hence it ensures the neutrality of the dust particle but still being attracted to the glass rod.

               And in the case of the negatively charged silk, the silk induces or gives positive charge to the dust particle which is neutral in charge. The face which is near to the silk gets positive charge and the other face becomes negative charge, again ensuring its neutrality and being attracted to the glass rod.

               This shows how both positive charged rod and negatively charged silk attracts the neutral dust particle.

this would be about 43%

conservation of mass

mass before something happens = mass afterwards