From the time I started keeping records in 2011 until 2018 I averaged at least 2 40% silver halves per box. In 2019 the average took a nosedive, and now it’s closer to 1 silver every 4or 5 boxes. Definitely not worth the time, I just continue more out of habit than anything.
The thing is that the average number of silver per box is usually far different from the 'typical box'. It's like the difference between the mean (average), the median (midway point between highest and lowest), and the mode (most common).
Take 2019 for instance.
In my case, I had the following ...
22 skunks
8 with 1 silver (6 @ 40%, 2 @ 90%)
3 with 2 silver (3 @ 2 x 40%)
5 with 3 silver (2 @ 3 x 40%, 2 @ 2 x 40% + 1 x 90%, and 1 @ 1 x 40% + 2 x 90%)
1 with 4 silver (1 @ 1 x 40% + 3 x 90%)
1 with 5 silver (1 @ 5 x 40%)
1 with 6 silver (1 @ 3 x 40% + 3 X 90%)
2 with 11 silver (1 @ 11 x 40% and 1 @ 7 x 40% + 4 x 90%)
1 with 14 silver (1 @ 10 x 40% + 4 x 90%)
1 with 19 silver (1 @ 10 x 40% + 9 x 90%)
1 with 22 silver (1 @ 14 x 40% + 8 x 90%)
1 with 26 silver (1 @ 26 x 40%)
So, statistically, the median box had 1 (40%) silver, the mode was a skunk, but the median had 3.1 silver (2.3 x 40% + 0.8 x 90%) which comes closest to the box with 2 x 40% + 1 x 90%)
My experience with half dollar boxes is "when it rains, it pours" but it's 'dry' far, far more often than it's 'wet').