The level of technology at the time was that random polymerization in vitro (that is, in a testtube with enzymes, buffers, and whatever nucleotides the scientist put into the tube) was possible, but precise construction of synthetic mRNAs wasn't an option.
So, scientists created synthetic mRNAs that contained only, say, uracil and cytosine. To distinguish between U and C content of each codon, they ensured that the proportion of U would not equal C. Thus, they knew if 80% C and 20% U were used, the most common codon would be CCC and the least common would be UUU. The number of CCC would be 0.83 and UUU would be 0.23.
Using this logic, answer the following question:
Try this for yourself before accessing the answer below ...