i think the places where you find yourself needing to use "heavy" calculations are:

1. figuring out a square root that you shouldve memorized

2. using plugin but not using easy to work with numbers

3. trying to find a huge number in a large sequence without finding some way to reduce it

4. forgetting some interest formulas so you have to multiply the years/months out.

Theres probably a few more but most of the time if you know the shortcuts you really dont need to do much calculation at all.

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