According to Chargaff’s rule,
A+G = T+C
I.e., The amount of guanine is equal to cytosine, and the amount of adenine is equal to thymine.
C = 30%
Therefore, G = 30%
Out of 100% of bases, C and G make up the 60%.
Since A = T
A = T = 20%
Therefore, purines, adenine and guanine make up the 50% of the bases.
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