If Adenine makes 30% of the DNA molecule, what will be the percentage of Thymine, Guanine and Cytosine in it?

DNA is composed of four nitrogenous bases that pair up in a double‑helix: adenine (A) always pairs with thymine (T), and guanine (G) always pairs with cytosine (C). Because the two strands are complementary, the amount of each base on one strand must equal the amount of its complementary base on the opposite strand.

Given that adenine makes up 30 % of the nucleotides, its complementary base thymine must also constitute 30 % of the nucleotides.

After accounting for A and T, the remaining proportion of the DNA is 100 % − 30 % − 30 % = 40 %. This remaining 40 % is shared equally between the G–C pair because no other information suggests an imbalance. Therefore:

• Guanine (G) = 40 % ÷ 2 = 20 %
• Cytosine (C) = 40 % ÷ 2 = 20 %

Thus the percentages are:

Thymine (T) : 30 % ; Guanine (G) : 20 % ; Cytosine (C) : 20 %