According to Chargaff’s rules, thymine has the same abundance as adenine in double-stranded DNA.
The relationship follows complementary base pairing: adenine pairs with thymine, while cytosine pairs with guanine. Therefore, in a typical double-stranded DNA sample, the percentage of adenine equals the percentage of thymine, and the percentage of cytosine equals the percentage of guanine.
Erwin Chargaff and colleagues established these base-composition patterns in the late 1940s and early 1950s. Their observations challenged the idea that DNA was a monotonous, repetitive molecule and helped provide important clues for the double-helix model.
These rules apply to double-stranded DNA, not necessarily to single-stranded DNA or RNA. RNA commonly uses uracil instead of thymine, so substituting uracil into this question would describe a different nucleic acid.