Question: how to calculate the percentage of guanine?
Answer: We know Adenine pairs with Thymine,and Cytosine pairs with Guanine.So there must be equal amounts of A and T,and equal amounts of C and G. We have 68% left... since there are equal amounts of C and G,68 will be divided by 2,giving 34% of Cytosine and Guanine each. So A=16%,T=16%,C=34% and G=34%.