3. in double stranded dna, 13% of the strand is found to be adenine. how much would you expect cytosine to be present?

Chargaff's rules state that the amount of guanine should be equal to cytosine and the amount of adenine should be equal to thymine because of how the base pairs match up. Thus another 13% is thymine. This leaves 74% of the DNA to be composed of cytosine and guanine, which they split equally. Thus, 37% percent of the DNA should be cytosine.