Hi,
In the video, I get that we’re approximating the slope of the curve based off a triangle, and I get that dividing by 0.2 is the same as dividing by 1/5 is the same as multiplying by 5 (though it might be nice to toss a quick aside into the video about reciprocals, as that did throw me for a loop).
However, what I’m wondering is whether it was intentional or a common practise to add a smidge or “round up” the answer in these cases, to account for the fact that you’re inherently underestimating the true answer due to how the approximation is being derived.
The reason I ask is, well, 18 * 5 = 90, not 91.
This left me scratching my head a bit as to whether it was an error or ‘typo’ by the instructor, or if he was simply modeling something that is commonly done but not explicitly stated (as with the unexplained but perfectly valid use of a reciprocal).