If a strand of DNA has 45% A, what percent will be C?

Explanation:

There is a method to calculating base percentages known as Chargaff's Rule. It states:

We know the DNA has 45% Adenine or A.

Adenine always pairs equally with Thymine. In other words, the percentage of adenine equals the percentage of thymine (45% Thymine or T).

Subtract 90% from both sides.

Cytosine(C) and Guanine(G) pair equally and their percentages will be equal. We can divide 10% by 2.

The percentage of Cytosine or C is 5 percent.