Each member of a class sampled a piece of ptc testing paper. thirty people sampled the chemical.

twenty persons were tasters. how many had homozygous genes?

10-30
10
10-20
0-10

Assuming that the trait of being able to taste the sample is a dominant trait, then the tasters have at least one of that dominant trait and the people who were not tasters had the homozygous genes for the recessive trait. Therefore, the answer is
10 - 30