The probability of at least one child inheriting the disease can be given by
P(X ≥ 1) = 1 - P(X = 0). This is because the only choice other than at least one child inheriting the disease is that no children get it.
Since there is a 70% or 0.7 chance that each child will inherit it, there is a 30% or 0.3 chance that they will not. This gives us
1 - P(X = 0) = 1 - (0.3)(0.3)(0.3) = 1 - 0.027 = 0.973
There is a 97.3% chance that at least one of the children will get the disease from their mother.
