Explanation: Following Chargaff's ratio that describes the ration of purines to pyrimidines as 1:1, if there are 23 purines, it follows that there should be 23 pyrimidines; 15 Thymines should therefore be hydrogen bonded to 15 Adenines by complementary base pairing.
We are then left with 8 nucleotides composed of guanines and cytosines in complementary base pairs. This means that half that number (4) should be guanines and the rest cytosines.
