Challenge 1: Diagnosing an Argument-Separator Error — Solution Walkthrough

Steps:
  1. Type =SUM(A1,A2,A3) into a cell.
  2. If it errors (commonly a syntax error, since Calc doesn't
     recognise the comma as an argument separator under some
     locales), open Tools > Options > Calc > Formula.
  3. Check the "Formula syntax" / separator settings to find which
     character your installation actually expects between arguments
     — comma or semicolon.
  4. If semicolon is what's expected, rewrite the formula as
     =SUM(A1;A2;A3).

Why the exact same underlying formula might need a different separator on a different computer:

The argument separator isn't a fixed property of Calc itself — it's
inherited from LibreOffice's own regional/locale settings, which can
differ from one installation to the next depending on the system's
configured region and language settings. Two people running the exact
same version of LibreOffice Calc, on two differently-configured
systems, can genuinely need different separator characters for the
identical underlying formula to be accepted — this is a configuration
difference, not a version or feature difference between the two
computers.

WHY THIS WORKS AS AN ANSWER
------------------------------
This is exactly the concrete, hands-on version of this chapter's own
central gotcha: the separator isn't a universal Calc rule to memorise
once, it's a setting worth checking (Tools > Options > Calc >
Formula) the moment a formula that "should" work produces an
unexpected syntax error.