Ans: $432$
Let $x$ and $y$ be the number of regular tickets and concessionary tickets sold respectively.
Let $x$ and $y$ be the number of regular tickets and concessionary tickets sold respectively.
$\left\{ \begin{array}{ll}
x = 5y & \ldots \textstyle\unicode{x2460} \\
126x + 78y = 50\ 976 & \ldots \textstyle\unicode{x2461}
\end{array} \right.$
Sub. $\textstyle\unicode{x2460}$ into $\textstyle\unicode{x2461}$, we have
$\begin{array}{rcl}
126(5y) +78y & = & 50\ 976 \\
708y & = & 50\ 976 \\
y & = & 72
\end{array}$
Sub. $y = 72$ into $\textstyle\unicode{x2460}$, we have
$\begin{array}{rcl}
x & = & 5(72) \\
x & = & 360
\end{array}$
Therefore, $360$ regular tickets and $72$ concessionary tickets sold that day.
Hence, the total number of admission tickets sold that day
$\begin{array}{cl}
= & 360 + 72 \\
= & 432
\end{array}$
