#### Answer

$0.8797$

#### Work Step by Step

We know that $probability=\frac{number \ of \ good \ outcomes}{number\ of\ all\ outcomes}$ and by the inclusion-exclusion principle:$P(A \cup B)=P(A)+P(B)-P(A\cap B)$. A:responded
B:his/her age is between 18 and 21. By checking the data:
$P(A)=\frac{1049}{1205}$
$P(B)=\frac{84}{1205}$
$P(A\cap B)=\frac{73}{1205}$
Therefore the probability of the person responding or his/her age being between 18 and 21: $P(A \cup B)=\frac{1049}{1205}+\frac{84}{1205}-\frac{73}{1205}=\frac{1060}{1205}\approx0.8797$