G9.3 If the $r^{\text {th }}$ day of May in a year is Friday and the $n^{\text {th }}$ day of May in the same year is Monday, where $15<n<25$, find $n$.
Reference: 1984 FG6.3, 1987 FG8.4, 1988 FG10.2
$3^{\text {rd }}$ May is Friday
$17^{\text {th }}$ May is Friday
$\Rightarrow 20^{\text {th }}$ May is Monday
$\Rightarrow n=20$