If you performed a pcr experiment starting with only one copy of double-stranded dna, approximately how many dna molecules would be present in the reaction tube after 19 cycles of amplification?

The formular used for estimating the number of DNA copies after a particular number of cycle is 2^n, where n is the number of cycle. From the question given, number of cycle is 19. So, we have 2^19 = 524,288.
Therefore, after 19 cycles, there will be 524, 288 copies of DNA molecules.

They must use the scientific method