If both electrons as well as holes are present the conductivities add. This is because under the effect of an applied electric field the holes as well as electrons flow in opposite directions as well as a negative charge moving in the (say) +z direction is equivalent to a positive charge moving in the -z direction.
Presume that in a certain semiconductor the ratio of electronic mobility, µe, to hole mobility, µh, is equal to 10, the density of holes is Nh=1020 m-3, as well as the density of electrons is Ne=10-19 m-3. The measured conductivity is 0.455 ohm-1.
Compute the motilities