Yup, and most electronics worldwide are still based on 0.1 inch increments.
I’m a designer and had to learn points and pico in art school. Those are inch based too (and totally useless in digital layouts). Metric is so easy that we all get it and use it when it makes sense. Largely with 3D printing and automotive fasteners (yeah even most of the “American” cars).
The real problem is the US and UK dominated manufacturing, and electronics in the early days and both used imperial units (though not always the same units). And because of that old used machine tools are all inch standard and how we learn and do hobbies. That and metric hardware is way more expensive in the states. I can get 1/3 of the fasteners in metric for the same money.
I’m glad I wasn’t the only one teased into trying to solve this. If you plot them on a straight line it’s a fairly straightforward 10". But the problem doesn’t tell you that, so yes, I don’t think we have enough information to solve
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