Answer
$P(both~same~age~category)=\frac{5773}{7285}\approx0.7925$
Work Step by Step
The sample space: $124+619+39+290+5628+480+4+80+21=7285$ cases. That is:
$N(S)=7285$
Now:
$N(both~Less~Than~18)=124$
$N(both~At~Least~18)=5628$
$N(both~Unknown~age)=21$
$P(both~same~age~category)=P(both~Less~Than~18~or~both~At~Least~18~or~both~Unknown~age)=P(both~Less~Than~18)+P(both~At~Least~18)+P(both~Unknown~age)=\frac{N(both~Less~Than~18)}{N(S)}+\frac{N(both~At~Least~18)}{N(S)}+\frac{N(both~Unknown~age)}{N(S)}=\frac{124}{7285}+\frac{5628}{7285}+\frac{21}{7285}=\frac{5773}{7285}\approx0.7925$
