Cytosine makes up 42% of the nucleotides in a sample of dna from an organism. Approximately what percentage of the nucleotides in this sample will be thymine?

8%

Explanation:

DNA is a double-stranded molecule made up of nucleotides: A, T, G, and C. According to Chargaff, A + T + G + C = 100%, where Adenine (A) pairs with Thymine (T) while Guanine (G) pairs with Cytosine (C).

Since G pairs with C and A with T, there must be equal proportions of each nuceleotide pair i. e. A=T, G=C

If C = 42%, G is also 42%

We then have, 42 + 42 + A + T = 100

84 + A + T = 100

A + T = 100 - 84

A + T = 16%

If A and T is collectively 16% and each must contain equal proportion, therefore, A=T = 16/2 = 8%.

Hence, proportion of Adenine and Thymine in that DNA is 8%.