Answer
$P(E)=0.5$
If the husband and wife have 4 children, we would expect that two will not have sickle-cell anemia but will be carriers.
Work Step by Step
Event = "the offspring will not have sickle-cell anemia but will be a carrier" = {Ss, sS}. So, $N(E)=2$.
The sample space: S = (SS, Ss, sS, ss}. So, $N(S)=4$.
$P(E)=\frac{N(E)}{N(S)}=\frac{2}{4}=0.5$
