When decoding the cherry genome, it was found that in a fragment of a DNA molecule, the proportion of nucleotides

When decoding the cherry genome, it was found that in a fragment of a DNA molecule, the proportion of nucleotides with thymine is 40%. Using Chargaff’s rule describing the quantitative ratios between different types of nitrogenous bases in DNA (G + T = A + C), calculate the amount (in%) in this sample of nucleotides with cytosine.

Adenine (A) is complementary to thymine (T), and guanine (G) is complementary to cytosine (C), therefore the number of complementary nucleotides is the same; Chargaff’s rule: (A + T) + (G + C) = 100%
By condition T = 40%
G + C = 100% – (40% + 40%) = 20%
C = G = 20%: 2 = 10%