In humans, the percentage of A in a DNA sample is 30 %. By Chargaff's rule, the percentage of G is

1. Chargaff's rule: A = T and G = C; total A+T+G+C = 100 %. 2. Given A = 30 %, T = 30 %. Remaining for G + C = 40 %. 3. Since G = C, each is 20 %. _Source: Maharashtra Balbharati Std XII Biology, Ch 4 "Molecular Basis of Inheritance" §4.3_