If dna of an organism contains 20% adenine, what is its percentage of guanine?

Adenine = A
Thymine = T
Guanine= G
Cytosine= C

A and T always pair together (so there are equal numbers of A and T)
G and C always pair togehter (so there are equal numbers of G and C).

20% A means there must also be 20%T.

20%+20%=40%.
100%-40%=60%

So that means that there is 60% C and G, and because there are equal numbers of both, you do 60% divided by 2, so get 30%.

Therefore, percentage of Guanine = 30 %

:)

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