Nothing at all makes the French person wrong, if the math adds up. I'm not talking about culture at all, it's just an example, like launching a rocket mentioned earlier in the thread. You seem a little angry, you ok?

To put it another way, forget about the equation. The "required" answer to launch the rocket in the example at the start of this thread is 7, not 9. Could we conceivably write and read math in a different order? Yeah absolutely, but if we write math the same and two people read it differently, then there's too much rocket fuel and it explodes on launch. That's why we have a standard for reading back these equations so that we can all get to the same answer.

In your example, you're talking about if the 'agreed language' of math was different, the other answer would be correct. But, if the required answer for this scenario was 7, the actual calculation would be written differently.

It's like if you have a room full of people speaking English, and one dude who only speaks French. It's not that French is wrong, but they're not going to be understanding each other.

The 250mm increments are actually 6 slices, so each rectangular slice must only be about 4cm wide, 20cm long