It may be inferred from the amount of a controlled substance or substances possessed by an offender, along with other relevant facts surrounding the arrest, that the controlled substance or substances were possessed with the purpose of selling or otherwise dispensing. It may be inferred from circumstances indicating a casual exchange among individuals of a small amount of a controlled substance or substances that the controlled substance or substances so exchanged were possessed not with the purpose of selling or otherwise dispensing in violation of §39-17-417(a). The inferences shall be transmitted to the jury by the trial judge's charge, and the jury will consider the inferences along with the nature of the substance possessed when affixing the penalty.