What can he assume about the number of adenine

Answer: knowing that the number of adenine will be always equal to the number of thymine.

Explanation:On the basis of base pairing rule, the purine bases bonds with the pyrimidine bases. This takes place as the configurations of pyrimidine and purine bases permit formation of hydrogen bonding between the two.

The base pairing rule suggests that the pairing of adenine takes place only with thymine and pairing of guanine takes place only with cytosine. Two hydrogen bonds are produced between an adenine and thymine base pair, while three hydrogen bonds are produced between a guanine and cytosine base pair.