If a DNA Sample Were Composed of 10% Thymine,what Would

Question

If a DNA sample were composed of 10% thymine,what would be the percentage of guanine?
A)10
B)20
C)40
D)80
E)impossible to tell from the information given

Accepted Answer

In DNA, the amount of adenine always equals the amount of thymine, and the amount of guanine always equals the amount of cytosine. Therefore, if the DNA sample has 10% thymine, it must also have 10% adenine. This leaves 80% of the DNA composed of guanine and cytosine. Since guanine and cytosine are always present in equal amounts, the answer is 80%/2 = 40% guanine.