Update cheatsheets

linux/arithmetic

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+---
+syntax: markdown
+tags: [tldr, linux]
+source: https://github.com/tldr-pages/tldr.git
+---
+# arithmetic
+
+> Quiz on simple arithmetic problems.
+> More information: <https://manpages.debian.org/latest/bsdgames/arithmetic.6.en.html>.
+
+- Start an arithmetic quiz:
+
+`arithmetic`
+
+- Specify one or more arithmetic [o]peration symbols to get problems on them:
+
+`arithmetic -o {{+|-|x|/}}`
+
+- Specify a range. Addition and multiplication problems would feature numbers between 0 and range, inclusive. Subtraction and division problems would have required result and number to be operated on, between 0 and range:
+
+`arithmetic -r {{7}}`