Rediphile, 1 year ago

It’s not arbitrary. Really try to think about the problem at hand. The ‘why’ is quite apparent. Ask yourself why did they go with 99+1+98+2… in the first place? And why is that the same as 101+101…? What was the benefit of simplifying it to that? How did it save the student time?

You can deduce this yourself and literally no memorization is involved to figure this out. No formulas needed either.