the strand is found to contain 30 % adenine so we going to have 27 percent thymine and 20% cytosine
as adenine is complementary to thymine,the percentage of thymine is 20% out of 100% 40%is adenine and thymine(20%A +20%T)the rest is 60% cytosine is complementary to guanine so the percentage of cytosine and guanine is 30%and 30%
cytosine pairs with only guanine.....therefore % adenine=%thymine=30% which totally makes 60% of the bases......% of cytosine=%of guanine=(40/2)%=20%
To answer this question, remember this: in DNA, adenine always pairs with thymine, and cytosine always pairs with guanine. Also, in a normal DNA molecule, all of the bases are paired. If 20% of the bases in DNA are adenine, then it follows that another 20% must be thymine, because adenine always pairs with thymine. Adding both percentages up, we get 40% of the DNA bases being adenine and thymine. That means the remaining 60% of the bases in the DNA molecule are cytosine and guanine. Using the same reasoning above, the proportions of cytosine and guanine must be equal because cytosine always pairs with guanine. Therefore, cytosine and guanine each compose 30% of the DNA molecule.
30 %. Adenine pairs with thymine - therefore if 20% is A, another 20% percent will be T. Only two other bases are left, which form pairs: guanine and cytosine, in equal quantities. Therefore half of the remaining 60 percent will be guanine.
There are four bases in the DNA double helix: adenine, guanine, cytosine and thymine. An adenine in one strand always pairs with a thymine in the other strand. Similarly, a cytosine always pairs with a guanine. So the number of adenines always equals the number of thymines, and the number of cytosines always equals the number of thymines. The total number of bases must equal 100%. So if 30% of the bases are adenine, another 30% must be thymine because they always pair with each other. Thymine and adenine added together therefore make 60% of the bases. The remaining 40% must be cytosine plus guanine. If the number of cytosines must equal the number of guanines, the percentage of cytosines must be ....... well, you can work it out for yourself!
Human DNA contains about 30% each of adenine and thymine, and about 20% each of guanine and cytosine.