How to solve DNA sequence probability problems

Purines and Pyrimidines are nitrogenous bases that make up the two different kinds of nucleotide bases in DNA and RNA. The two-carbon nitrogen ring bases (adenine and guanine) are purines, while the one-carbon nitrogen ring bases (thymine and cytosine) are pyrimidines. #purines #Pyrimidines #DNA #RNA #Adenine #Guanine #thymine #Cytosine