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Notes on arithmetic, rounding, and the strange economics of calculator apps.
Why does 0.1 + 0.2 = 0.30000000000000004?
Because 0.1 has no exact form in binary, the same way 1/3 has none in decimal. What the machine really stores, why almost every calculator does this, and the arithmetic that does not.
Which calculator apps have no subscription?
Real prices from the live App Store listings. Also the finding we did not expect: the calculator with no ads at all is rated 3.02, and one full of them is rated 4.87.
How to split a bill with tip
An 84.50 bill, 18%, three people. The arithmetic, the mental shortcut, and the direction you have to round so the table does not come up two cents short.