DELIBERATELY WRONG — authored teaching counterexample

I joined projects to checks and counted the joined rows for both measures.
North has 4 projects, 4 checks and 3 passed checks. South has 2 projects,
2 checks and 1 passed check. West has 1 project, 1 check and 0 passed
checks. The full result therefore contains 7 projects and 7 checks,
with 4 passed checks.