If one strand of a DNA molecule contains 22% adenine, what percentage of the whole molecule is guanine?

Explanation

Chargaff's rule applies to the double stranded molecule, so A equals T and G equals C. With A at 22%, T is also 22%, leaving 100 minus 44 which is 56% shared equally between G and C, giving 28% guanine. The common error is to stop at 56% and forget that it is split between two bases.