Aproximately 1 in 28 people of ashkenazi jewish descent are tay-sachs carrier ... from this population, what is the probability neither is tay-sachs carrier?

If we randomly pick two persons from the population, each one will have a probability of 1-1/28=27/28 of being a non-carrier.

Thus for neither to be non-carrier, the probability is the product of the individual probabilities since the picks are assumed independent (with a large enough population).

Probability = (27/28) * (27/28) = 729/784

or approximately 0.930