4. (10 points) The ticket price for a friendly football match is 50 yuan. An hour before the game, there were still tickets left, so the price was reduced. As a result, the number of tickets sold increased by one-third, and the box office revenue increased by one-quarter. Therefore, the price of each ticket was reduced by ( ) yuan.
A. 10
B. $\frac{25}{2}$
C. $\frac{50}{3}$
D. 25
【Analysis】Let the original number of tickets sold be 1. According to the problem, the increased amount of money is $50 \times \frac{1}{4}=\frac{25}{2}$, which is the total money from one-third more tickets. Therefore, dividing by $\frac{1}{3}$ gives the price per ticket for the discounted part. Then, subtracting this from 50 gives the amount by which the price of each ticket has decreased.

【Solution】Let the original number of tickets sold be 1,
$$
\begin{array}{l}
50-50 \times \frac{1}{4} \div \frac{1}{3} \\
=50-\frac{75}{2} \\
=\frac{25}{2} \text { (yuan) }
\end{array}
$$

Answer: The price of each ticket decreased by $\frac{25}{2}$ yuan.
Therefore, the correct choice is: $B$.