19 Let $p$ and $q$ represent two consecutive prime numbers. For some fixed integer $n$, the set $\{n-1,3 n-19,38-5 n, 7 n-45\}$ represents $\{p, 2 p, q, 2 q\}$, but not necessarily in that order. Find the value of $n$.
19 Answer: (7)
Since $3 p+3 q=6 n-27, p+q=2 n-9$ which is odd. So $p=2, q=3$ and $n=7$.