The point is that you can’t observe anything without some kind of interaction. Even just looking at something requires bouncing light off of it.
We’re used to our observations seeming passive because light is often hitting the things anyways, but the double slit experiment forces the point because the subjects of the experiment are so small that even just using ways of observing them affects the outcome of the experiment.









It’s about 300 samples for an estimate of the distribution with a 95% confidence iirc. That’s assuming the samples are representative (unbiased) and 95% confidence doesn’t mean it’s within 95% of reality, but that 5% of tests run in such a way would be expected to be inaccurate (and there’s no way of knowing for sure which one this particular sample is because even a meta study will have such an error rate, though you can increase the confidence with more samples or studies, just never to 100% unless you study every possible sample, including future ones).