Not sure what to feel about this one, on one hand i get that it's infuriating when people are just not paying attention but at the same time i don't think that gives you the right to tamper with their stuff this way.

What I do in my head:
26 + 19 = 25 + 20 = 45
45²/45 = 45 (duh)
47 = 45 + 2
24 * 45 + 45 + 2 = 25 * 45 + 2 = 25 * 44 + 25 + 2 = 1100 + 27 = 1127.
And that's just one way of doing it. I don't claim my way is the best.

…So yeah, if you've practiced enough basic maths, there's no need to write anything.