Ans: $35$
Let $x$ and $y$ be the number of male and female passengers on the ferry respectively.
$\left\{ \begin{array}{ll}
y = x(1+40\%) & \ldots \unicode{x2460} \\
x = (y-24)(1+40\%) & \ldots \unicode{x2461}
\end{array}\right.$
Sub. $\unicode{x2461}$ into $\unicode{x2460}$, we have
$\begin{array}{rcl}
y & = & (y-24)(1+40\%)(1+40\%) \\
y & = & 1.96(y-24) \\
y & = & 1.96y -47.04 \\
0.96y & = & 47.04 \\
y & = & 49
\end{array}$
Sub. $y=49$ into $\unicode{x2460}$, we have
$\begin{array}{rcl}
49 & = & x(1+40\%) \\
1.4x & = & 49 \\
x & = & 35
\end{array}$
Therefore, there are $35$ male passengers on the ferry.
