The right answer is The number of adenine will be equal to the number of thymine.
Chargaff's rules indicate that the DNA of any cell or organism must have a ratio of 1 to 1 between purine bases and pyrimidine bases and, more specifically, that the amount of guanine is equal to the amount cytosine, and that the amount of adenine is equal to the amount of thymine. This trend is found in both strands of DNA.
He can assume that the number of adenine is always equal to the number of thymine because of the base pair rule. Adenine matches with the other purine pair, so it matches with thymine because it is the thing that t can have a hydrogen bond with. Hope it helps.
