4. (6 points) Arrange the numbers 1 to 25 in any order in a row, then subtract them sequentially from $1,2,3, \cdots, 25$, always subtracting the smaller number from the larger one. Among these 25 differences, the maximum number of even numbers is $\qquad$.
【Solution】Solution: According to the problem, we know:
To get the maximum number of even numbers, arrange them in an alternating pattern of odd and even, such as, $3, 4, 5 \cdots 25, 2, 1$, and then subtract them from
$1, 2, 3, \cdots, 25$ in sequence,
which results in: odd - odd $=$ even, even - even $=$ even
Therefore, the maximum number of even numbers is 25.
So the answer is: 25.