Final answer:
A single strand of RNA with 20% uracil implies an equal percentage of adenine (assuming internal base-pairing regions); the remaining 60% would be divided between cytosine and guanine, potentially as 30% each if there's no bias toward either base.
Step-by-step explanation:
If an RNA strand has 20% uracil (U), we can deduce the percentage of the other nucleobases - adenine (A), cytosine (C), and guanine (G). Since RNA is typically single-stranded and does not follow the strict base-pairing rule of DNA, we cannot simply say that adenine will also be 20%. Instead, we must consider that RNA can have non-uniform distributions of nucleotides.
However, if we assume that this RNA strand has base-pairing regions and follows a form of Chargaff's rules within those regions, we can predict that adenine (A) would also be 20% since A pairs with U. This leaves 60% for cytosine (C) and guanine (G). If there is no specific bias towards one of these other bases in this RNA sequence, they could be equally distributed, with 30% cytosine (C) and 30% guanine (G).