Total Women = 30
Descended from John ($f(J)$) = $16$
Descended from George ($f(G)$) = $17$
Not descended from either John or George = $5$
$\therefore$ Descended from either John or George ($f(J) \cup f(G)$ = $25$
Women are descended from both George and John = $f(G) \cap f(J)$
$f(G) \cup f(J) = f(G) + f(J) – f(J)\cap f(g)$
$25 = 17 + 16 – f(J)\cap f(G)$
$f(J) \cap f(G) = 33-25 = 8$