If 30% of a DNA sample is composed of thymine nucleotides, what percentage of the DNA sample would be composed of cytosine nucleotides?

20%

Explanation:

Pairing do occur between a purine and a pyrimidine base or a pyrimidine and a purine base where Adenine pairs with Thymine and Guanine pairs with Cytosine.

DNA(deoxyribonucliec acid) sample is usually compose of 100% nucleotide base,

Since 30% of the sample section is compose of thymine then Adenine the base pair will also be 30% this is because adenine will always pair with thymine and each will occur in equal quantity. Together, adenine and thymine compose 60% of the segment.

While the remaining 40% of the section is composed of guanine and cytosine pairs and since the two bases will be equal in quantity, 20% of the DNA section will be cytosine nucleotide.

true is the final answer!