In a DNA strand, the amount of Adenine equals the amount of Thymine, and the amount of Guanine equals the amount of Cytosine. So Adenine is your answer.
This principle is called Chargaff's rule. In double stranded DNA Thymine is always bound to Adenine while Cytosine is always bound with Guanine. Therefore the percentage of A will always equal the...
Every adenine in DNA will be paired to a thymine. However in RNA adenine is paired to uracil. So no - all else being equal since there is DNA and RNA in a body there will not be equal amounts.